When should I use double or single quotes in JavaScript

Question

console log  quot double quot    vs  console log  single    I see more and more JavaScript libraries out there using single quotes when handling strings  What are the reasons to use one over the other  I thought they re pretty much interchangeable

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Section 7 8 4 of the specification describes literal string notation  The only difference is that DoubleStringCharacter is  SourceCharacter but not double-quote  and SingleStringCharacter is  SourceCharacter but not single-quote   So the only difference can be demonstrated thusly    A string that  s single quoted    A string that s double quoted    So it depends on how much quote escaping you want to do  Obviously the same applies to double quotes in double quoted strings

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If you re doing inline JavaScript  arguably a  quot bad quot  thing  but avoiding that discussion  single quotes are your only option for string literals  I believe  E g   this works fine   lt a onclick  quot alert  hi    quot  gt hi lt  a gt   But you can t wrap the  quot hi quot  in double quotes  via any escaping method I m aware of  Even  amp quot  which would have been my best guess  since you re escaping quotes in an attribute value of HTML  doesn t work for me in Firefox    quot  won t work either because at this point you re escaping for HTML  not JavaScript  So  if the name of the game is consistency  and you re going to do some inline JavaScript in parts of your application  I think single quotes are the winner  Someone please correct me if I m wrong though

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After reading all the answers that say it may be be faster or may be have advantages  I would say double quotes are better or may be faster too because the Google Closure compiler converts single quotes to double quotes

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If you are using JSHint  it will raise an error if you use a double quoted string  I used it through the Yeoman scafflholding of AngularJS  but maybe there is somehow a manner to configure this  By the way  when you handle HTML into JavaScript  it s easier to use single quote  var foo     lt div class  quot cool-stuff quot  gt Cool content lt  div gt     And at least JSON is using double quotes to represent strings  There isn t any trivial way to answer to your question

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If you re doing inline JavaScript  arguably a  quot bad quot  thing  but avoiding that discussion  single quotes are your only option for string literals  I believe  E g   this works fine   lt a onclick  quot alert  hi    quot  gt hi lt  a gt   But you can t wrap the  quot hi quot  in double quotes  via any escaping method I m aware of  Even  amp quot  which would have been my best guess  since you re escaping quotes in an attribute value of HTML  doesn t work for me in Firefox    quot  won t work either because at this point you re escaping for HTML  not JavaScript  So  if the name of the game is consistency  and you re going to do some inline JavaScript in parts of your application  I think single quotes are the winner  Someone please correct me if I m wrong though

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There isn t any difference between single and double quotes in JavaScript  The specification is important  Maybe there are performance differences  but they are absolutely minimum and can change any day according to browsers  implementation  Further discussion is futile unless your JavaScript application is hundreds of thousands lines long  It s like a benchmark if a b   is faster than a   b    extra spaces  today  in a particular browser and platform  etc

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I think this is all a matter of convenience preference  I prefer double quote because it matches what C  has and this is my environment that I normally work in  C    JavaScript  Also one possible reason for double quotes over single quotes is this  which I have found in my projects code   French or some other languages use single quotes a lot  like English actually   so if by some reason you end up rendering strings from the server side  which I know is bad practice   then a single quote will render wrongly  The probability of using double quotes in a regular language is low  and therefore I think it has a better chance of not breaking something

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If you re dealing with JSON  it should be noted that strictly speaking  JSON strings must be double quoted  Sure  many libraries support single quotes as well  but I had great problems in one of my projects before realizing that single quoting a string is in fact not according to JSON standards

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Section 7 8 4 of the specification describes literal string notation  The only difference is that DoubleStringCharacter is  SourceCharacter but not double-quote  and SingleStringCharacter is  SourceCharacter but not single-quote   So the only difference can be demonstrated thusly    A string that  s single quoted    A string that s double quoted    So it depends on how much quote escaping you want to do  Obviously the same applies to double quotes in double quoted strings

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There is strictly no difference  so it is mostly a matter of taste and of what is in the string  or if the JavaScript code itself is in a string   to keep number of escapes low  The speed difference legend might come from PHP world  where the two quotes have different behavior

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There isn t any difference between single and double quotes in JavaScript  The specification is important  Maybe there are performance differences  but they are absolutely minimum and can change any day according to browsers  implementation  Further discussion is futile unless your JavaScript application is hundreds of thousands lines long  It s like a benchmark if a b   is faster than a   b    extra spaces  today  in a particular browser and platform  etc

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It is just a matter time for me  A few milliseconds lost of my life every time I have to press the Shift key before every time I m able to type  quot   I prefer   simply because you don t have to do it  Other than that  you can escape a   inside single quotes with backslash     console log  Don  t lose time        quot Don t lose time quot

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I am not sure if this is relevant in today s world  but double quotes used to be used for content that needed to have control characters processed and single quotes for strings that didn t  The compiler will run string manipulation on a double quoted string while leaving a single quoted string literally untouched  This used to lead to  good  developers choosing to use single quotes for strings that didn t contain control characters like  n or  0  not processed within single quotes  and double quotes when they needed the string parsed  at a slight cost in CPU cycles for processing the string

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Talking about performance  quotes will never be your bottleneck  However  the performance is the same in both cases  Talking about coding speed  if you use   for delimiting a string  you will need to escape  quot  quotes  You are more likely to need to use  quot  inside the string  Example     JSON Objects  var jsonObject      quot foo quot   quot bar quot         HTML attributes  document getElementById  quot foobar quot   innerHTML     lt input type  quot text quot  gt     Then  I prefer to use   for delimiting the string  so I have to escape fewer characters

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The most likely reason for use of single vs  double in different libraries is programmer preference and or API consistency  Other than being consistent  use whichever best suits the string  Using the other type of quote as a literal  alert  Say  quot Hello quot     alert  quot Say  Hello  quot     This can get complicated  alert  quot It s   quot game  quot  time  quot    alert  It  s  quot game quot  time      Another option  new in ECMAScript  6  is template literals which use the backtick character  alert  Use  quot double quot  and  single  quotes in the same string    alert  Escape the    back-tick character and the     dollar-brace sequence in a string     Template literals offer a clean syntax for  variable interpolation  multi-line strings  and more  Note that JSON is formally specified to use double quotes  which may be worth considering depending on system requirements

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One  silly  reason to use single quotes would be that they don t require you to hit the shift key to type them  whereas a double quote do    I m assuming that the average string doesn t require escaping  which is a reasonable assumption    Now  let s suppose every day I code 200 lines of code   Maybe in those 200 lines I have 30 quotes   Maybe typing a double quote takes 0 1 seconds more time than typing a single quote  because I have to hit the shift key    Then on any given day  I waste 3 seconds   If I code in this manner for 200 days a year for 40 years  then I ve wasted 6 7 hours of my life   Food for thought

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Talking about performance  quotes will never be your bottleneck  However  the performance is the same in both cases  Talking about coding speed  if you use   for delimiting a string  you will need to escape  quot  quotes  You are more likely to need to use  quot  inside the string  Example     JSON Objects  var jsonObject      quot foo quot   quot bar quot         HTML attributes  document getElementById  quot foobar quot   innerHTML     lt input type  quot text quot  gt     Then  I prefer to use   for delimiting the string  so I have to escape fewer characters

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Single Quotes I wish double quotes were the standard  because they make a little bit more sense  but I keep using single quotes because they dominate the scene  Single quotes   Airbnb Facebook Google Grunt Gulp js Node js npm  though not defined in the author s guide  Wikimedia WordPress Yandex  No preference   Three js  Double quotes   TypeScript Douglas Crockford D3 js  though not defined in  eslintrc  jQuery

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When using CoffeeScript I use double quotes  I agree that you should pick either one and stick to it  CoffeeScript gives you interpolation when using the double quotes   quot This is my   name  quot   ECMAScript  6 is using back ticks     for template strings  Which probably has a good reason  but when coding  it can be cumbersome to change the string literals character from quotes or double quotes to backticks in order to get the interpolation feature  CoffeeScript might not be perfect  but using the same string literals character everywhere  double quotes  and always be able to interpolate is a nice feature   This is my   name

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The difference is purely stylistic  I used to be a double-quote Nazi  Now I use single quotes in nearly all cases  There s no practical difference beyond how your editor highlights the syntax

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The most likely reason for use of single vs  double in different libraries is programmer preference and or API consistency  Other than being consistent  use whichever best suits the string  Using the other type of quote as a literal  alert  Say  quot Hello quot     alert  quot Say  Hello  quot     This can get complicated  alert  quot It s   quot game  quot  time  quot    alert  It  s  quot game quot  time      Another option  new in ECMAScript  6  is template literals which use the backtick character  alert  Use  quot double quot  and  single  quotes in the same string    alert  Escape the    back-tick character and the     dollar-brace sequence in a string     Template literals offer a clean syntax for  variable interpolation  multi-line strings  and more  Note that JSON is formally specified to use double quotes  which may be worth considering depending on system requirements

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You can use single quotes or double quotes  This enables you for example to easily nest JavaScript content inside HTML attributes  without the need to escape the quotes  The same is when you create JavaScript with PHP  The general idea is  if it is possible use such quotes that you won t need to escape  Less escaping   better code

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If you use PHP to generate JavaScript code you should use the following declaration  let value    quot  lt  php echo  This is my message   quot double quoted quot  -   single quoted     gt  quot    The output will be  This is my message   quot double quoted quot  -  single quoted   For some reasons it is recommend to use single quotes rather than double quotes in PHP  For the normal behaviour in JavaScript it is recommend to use single quotes   x000D   x000D  var value    This is my message   document getElementById  sample-text   innerHTML   value  x000D   lt span id  sample-text  gt  lt  span gt  x000D   x000D   x000D

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The best practice is to use double quotes   quot  quot   first and single quotes      if needed after  The reason being is that if you ever use server-side scripting you will not be able to pull content from a server  example SQL queries from a database  if you use singles quotes over double

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I d like to say the difference is purely stylistic  but I m really having my doubts  Consider the following example         Add trim   functionality to JavaScript          1  By extending the String prototype       2  By creating a  stand-alone  function     This is just to demonstrate results are the same in both cases         Extend the String prototype with a trim   method String prototype trim   function         return this replace    s   s   g               Stand-alone  trim   function function trim str        return str replace    s   s   g           document writeln String prototype trim   document writeln trim    In Safari  Chrome  Opera  and Internet Explorer  tested in Internet  Explorer  7 and Internet  Explorer  8   this will return the following  function          return this replace    s   s   g         function trim str        return str replace    s   s   g          However  Firefox will yield a slightly different result  function          return this replace    s   s   g   quot  quot      function trim str        return str replace    s   s   g   quot  quot       The single quotes have been replaced by double quotes   Also note how the indenting space was replaced by four spaces   This gives the impression that at least one browser parses JavaScript internally as if everything was written using double quotes  One might think  it takes Firefox less time to parse JavaScript if everything is already written according to this  standard   Which  by the way  makes me a very sad panda  since I think single quotes look much nicer in code  Plus  in other programming languages  they re usually faster to use than double quotes  so it would only make sense if the same applied to JavaScript  Conclusion  I think we need to do more research on this  This might explain Peter-Paul Koch s test results from back in 2003   It seems that single quotes are sometimes faster in Explorer Windows  roughly 1 3 of my tests did show a faster response time   but if Mozilla shows a difference at all  it handles double quotes slightly faster  I found no difference at all in Opera   2014  Modern versions of Firefox Spidermonkey don   t do this anymore

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The most likely reason for use of single vs  double in different libraries is programmer preference and or API consistency  Other than being consistent  use whichever best suits the string  Using the other type of quote as a literal  alert  Say  quot Hello quot     alert  quot Say  Hello  quot     This can get complicated  alert  quot It s   quot game  quot  time  quot    alert  It  s  quot game quot  time      Another option  new in ECMAScript  6  is template literals which use the backtick character  alert  Use  quot double quot  and  single  quotes in the same string    alert  Escape the    back-tick character and the     dollar-brace sequence in a string     Template literals offer a clean syntax for  variable interpolation  multi-line strings  and more  Note that JSON is formally specified to use double quotes  which may be worth considering depending on system requirements

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Just keep consistency in what you use  But don t let down your comfort level   quot This is my string  quot       -   quot I m invincible  quot      Comfortable     You can  t beat me       Uncomfortable     Oh  Yes  I can  quot beat quot  you       Comfortable     quot Do you really think  you can   quot beat  quot  me  quot      Uncomfortable     quot You re my guest  I can   quot beat  quot  you  quot      Sometimes  you ve to  P  You  re my guest too  I can  quot beat quot  you too       Sometimes  you ve to  P  ECMAScript  6 update Using template literal syntax   Be  quot my quot  guest  You re in complete freedom       Most comfort  D

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I would use double quotes when single quotes cannot be used and vice versa         singleQuotedValue             doubleQuotedValue         Instead of          singleQuotedValue               doubleQuotedValue

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I hope I am not adding something obvious  but I have been struggling with Django  Ajax  and JSON on this  Assuming that in your HTML code you do use double quotes  as normally should be  I highly suggest to use single quotes for the rest in JavaScript  So I agree with ady  but with some care  My bottom line is  In JavaScript it probably doesn t matter  but as soon as you embed it inside HTML or the like you start to get troubles  You should know what is actually escaping  reading  passing your string  My simple case was  tbox innerHTML   tbox innerHTML     lt div class  quot thisbox des quot  style  quot width 210px  quot  onmouseout  quot clear   quot  gt  lt a href  quot  this thislist                        myThis i  pk    quot  gt  lt img src  quot  site media                        myThis i  fields thumbnail    quot  height  quot 80 quot  width  quot 80 quot  style  quot float left  quot  onmouseover  quot showThis                        myThis i  fields left                           myThis i  fields right                             myThis i  fields title       quot  gt  lt  a gt  lt p style  quot float left width 130px height 80px  quot  gt  lt b gt                        myThis i  fields title    lt  b gt                         myThis i  fields description    lt  p gt  lt  div gt    You can spot the   in the third field of showThis  The double quote didn t work  It is clear why  but it is also clear why we should stick to single quotes    I guess    This case is a very simple HTML embedding  and the error was generated by a simple copy paste from a  double quoted  JavaScript code  So to answer the question  Try to use single quotes while within HTML  It might save a couple of debug issues

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For me  if I code in a Vim editor and if something is enclosed in single quotes  I can double-click to select only the text within the quotes  Double quotes  on the other hand  include the quote marks which I find annoying when I want to do some quick copy and pasting  E g   myVar  double-click in the Vim editor copies   gt myVar lt   quot myVar quot  literally copies   gt  quot myVar quot  lt  and when I paste  I have to delete the quote marks on either side

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Section 7 8 4 of the specification describes literal string notation  The only difference is that DoubleStringCharacter is  SourceCharacter but not double-quote  and SingleStringCharacter is  SourceCharacter but not single-quote   So the only difference can be demonstrated thusly    A string that  s single quoted    A string that s double quoted    So it depends on how much quote escaping you want to do  Obviously the same applies to double quotes in double quoted strings

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Now that it s 2020  we should consider a third option for JavaScript  The single backtick for everything  This can be used everywhere instead of single or double quotes  It allows you to do all the things   Embed single quotes inside of it   It s great    Embed double quotes inside of it   It s  quot really quot  great    Use string interpolation   It s  quot   better  quot  than great    It allows multiple lines    This Makes JavaScript Better      It also doesn t cause any performance loss when replacing the other two  Are backticks      slower than other strings in JavaScript

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I prefer to use the single quote     It is easier to type and looks better  Also  let   s remember that straight quotes  single and double  are a mistake in good typography  Curly quotes are preferable  so instead of escaping straight quotes I prefer to use the correct characters  const message    That  s a   magic   shoe      This is wrong const message    That   s a    magic    shoe      This is correct  https   practicaltypography com straight-and-curly-quotes html Can someone add a smart-quote feature to Visual Studio Code  please

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For use of JavaScript code across different languages  I ve found single quotes to consistently require less code tweaking   Double quotes support multi-line strings

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Section 7 8 4 of the specification describes literal string notation  The only difference is that DoubleStringCharacter is  SourceCharacter but not double-quote  and SingleStringCharacter is  SourceCharacter but not single-quote   So the only difference can be demonstrated thusly    A string that  s single quoted    A string that s double quoted    So it depends on how much quote escaping you want to do  Obviously the same applies to double quotes in double quoted strings

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For use of JavaScript code across different languages  I ve found single quotes to consistently require less code tweaking   Double quotes support multi-line strings

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There is strictly no difference  so it is mostly a matter of taste and of what is in the string  or if the JavaScript code itself is in a string   to keep number of escapes low  The speed difference legend might come from PHP world  where the two quotes have different behavior

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I prefer to use the single quote     It is easier to type and looks better  Also  let   s remember that straight quotes  single and double  are a mistake in good typography  Curly quotes are preferable  so instead of escaping straight quotes I prefer to use the correct characters  const message    That  s a   magic   shoe      This is wrong const message    That   s a    magic    shoe      This is correct  https   practicaltypography com straight-and-curly-quotes html Can someone add a smart-quote feature to Visual Studio Code  please

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I would use double quotes when single quotes cannot be used and vice versa         singleQuotedValue             doubleQuotedValue         Instead of          singleQuotedValue               doubleQuotedValue

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There are people that claim to see performance differences  old mailing list thread  But I couldn t find any of them to be confirmed  The main thing is to look at what kind of quotes  double or single  you are using inside your string  It helps to keep the number of escapes low  For instance  when you are working with HTML content inside your strings  it is easier to use single quotes so that you don t have to escape all double quotes around the attributes

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Examining the pros and cons   In favor of single quotes   Less visual clutter  Generating HTML  HTML attributes are usually delimited by double quotes     x000D   x000D  elem innerHTML     lt a href      url      gt Hello lt  a gt    x000D   x000D   x000D   However  single quotes are just as legal in HTML    x000D   x000D  elem innerHTML     lt a href      url      gt Hello lt  a gt    x000D   x000D   x000D    Furthermore  inline HTML is normally an anti-pattern  Prefer templates    Generating JSON  Only double quotes are allowed in JSON     x000D   x000D  myJson       hello world   true     x000D   x000D   x000D    Again  you shouldn   t have to construct JSON this way  JSON stringify   is often enough  If not  use templates   In favor of double quotes   Doubles are easier to spot if you don t have color coding  Like in a console log or some kind of view-source setup  Similarity to other languages  In shell programming  Bash etc    single-quoted string literals exist  but escapes are not interpreted inside them  C and Java use double quotes for strings and single quotes for characters  If you want code to be valid JSON  you need to use double quotes    In favor of both  There is no difference between the two in JavaScript  Therefore  you can use whatever is convenient at the moment  For example  the following string literals all produce the same string    x000D   x000D       He said    Let s go     x000D       He said   Let  s go    x000D       He said    Let  s go     x000D       He said    Let  s go     x000D   x000D   x000D    Single quotes for internal strings and double for external  That allows you to distinguish internal constants from strings that are to be displayed to the user  or written to disk etc    Obviously  you should avoid putting the latter in your code  but that can   t always be done

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As stated by other replies  they are almost the same  But I will try to add more   Some efficient algorithms use character arrays to process strings  Those algorithms  browser compiler  etc   would see  quot    34  first before     39  therefore saving several CPU cycles depending on your data structure   quot  is escaped by anti-XSS engines

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There is no one better solution  however  I would like to argue that double quotes may be more desirable at times    Newcomers will already be familiar with double quotes from their language   In English  we must use double quotes   to identify a passage of quoted text   If we were to use a single quote    the reader may misinterpret it as a contraction   The other meaning of a passage of text surrounded by the   indicates the  colloquial  meaning   It makes sense to stay consistent with pre-existing languages  and this may likely ease the learning and interpretation of code  Double quotes eliminate the need to escape apostrophes  as in contractions    Consider the string   I m going to the mall   vs  the otherwise escaped version   I  m going to the mall   Double quotes mean a string in many other languages   When you learn a new language like Java or C  double quotes are always used  In Ruby  PHP and Perl  single-quoted strings imply no backslash escapes while double quotes support them    JSON notation is written with double quotes    Nonetheless  as others have stated  it is most important to remain consistent

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The best practice is to use double quotes   quot  quot   first and single quotes      if needed after  The reason being is that if you ever use server-side scripting you will not be able to pull content from a server  example SQL queries from a database  if you use singles quotes over double

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If you re jumping back an forth between JavaScript and C   it s best to train your fingers for the common convention which is double quotes

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Strictly speaking  there is no difference in meaning  so the choice comes down to convenience  Here are several factors that could influence your choice   House style  Some groups of developers already use one convention or the other  Client-side requirements  Will you be using quotes within the strings   See Ady s answer   Server-side language  VB NET people might choose to use single quotes for JavaScript so that the scripts can be built server-side  VB NET uses double-quotes for strings  so the JavaScript strings are easy to distinguished if they use single quotes   Library code  If you re using a library that uses a particular style  you might consider using the same style yourself  Personal preference  You might think one or other style looks better

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Now that it s 2020  we should consider a third option for JavaScript  The single backtick for everything  This can be used everywhere instead of single or double quotes  It allows you to do all the things   Embed single quotes inside of it   It s great    Embed double quotes inside of it   It s  quot really quot  great    Use string interpolation   It s  quot   better  quot  than great    It allows multiple lines    This Makes JavaScript Better      It also doesn t cause any performance loss when replacing the other two  Are backticks      slower than other strings in JavaScript

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Single Quotes I wish double quotes were the standard  because they make a little bit more sense  but I keep using single quotes because they dominate the scene  Single quotes   Airbnb Facebook Google Grunt Gulp js Node js npm  though not defined in the author s guide  Wikimedia WordPress Yandex  No preference   Three js  Double quotes   TypeScript Douglas Crockford D3 js  though not defined in  eslintrc  jQuery

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I think this is all a matter of convenience preference  I prefer double quote because it matches what C  has and this is my environment that I normally work in  C    JavaScript  Also one possible reason for double quotes over single quotes is this  which I have found in my projects code   French or some other languages use single quotes a lot  like English actually   so if by some reason you end up rendering strings from the server side  which I know is bad practice   then a single quote will render wrongly  The probability of using double quotes in a regular language is low  and therefore I think it has a better chance of not breaking something

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Just to add my two cents  In working with both JavaScript and PHP a few years back  I ve become accustomed to using single quotes so I can type the escape character      without having to escape it as well  I usually used it when typing raw strings with file paths  etc  Anyhow  my convention ended up becoming the use of single quotes on identifier-type raw strings  such as if  typeof s     string        in which escape characters would never be used - ever   and double quotes for texts  such as  quot Hey  what s up  quot    I also use single quotes in comments as a typographical convention to show identifier names  This is just a rule of thumb  and I break off only when needed  such as when typing HTML strings   lt a href  quot   quot  gt  like so  lt a gt    though you could reverse the quotes here also   I m also aware that  in the case of JSON  double quotes are used for the names - but outside that  personally  I prefer the single quotes when escaping is never required for the text between the quotes - like document createElement  div    The bottom line is  and as some have mentioned alluded to  to pick a convention  stick with it  and only deviate when necessary

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Personally I prefer single quotes for the sake of readability  If I m staring at code all day it s easier to see the words with just single quotes as opposed to double quotes   Easier to read as demonstrated here    easy to read    harder to read     hardest to read

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One more thing that you might want to consider as a reason for the shift from double quotes to single quotes is the increase in popularity of server side scripts  When using PHP you can pass variables and parse JavaScript functions using strings and variables in PHP  If you write a string and use double quotes for your PHP you won t have to escape any of the single quotes and PHP will automatically retrieve the value of the variables for you  Example I need to run a JavaScript function using a variable from my server  public static function redirectPage   pageLocation         echo  quot  lt script type  text javascript  gt window location     pageLocation   lt  script gt  quot      This saves me a lot of hassle in having to deal with joining strings  and I can effectively call a JavaScript from PHP  This is only one example  but this may be one of several reasons why programmers are defaulting to single quotes in JavaScript  Quote from PHP documents   The most important feature of double-quoted strings is the fact that variable names will be expanded  See string parsing for details

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The difference is purely stylistic  I used to be a double-quote Nazi  Now I use single quotes in nearly all cases  There s no practical difference beyond how your editor highlights the syntax

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There is strictly no difference  so it is mostly a matter of taste and of what is in the string  or if the JavaScript code itself is in a string   to keep number of escapes low  The speed difference legend might come from PHP world  where the two quotes have different behavior

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Strictly speaking  there is no difference in meaning  so the choice comes down to convenience  Here are several factors that could influence your choice   House style  Some groups of developers already use one convention or the other  Client-side requirements  Will you be using quotes within the strings   See Ady s answer   Server-side language  VB NET people might choose to use single quotes for JavaScript so that the scripts can be built server-side  VB NET uses double-quotes for strings  so the JavaScript strings are easy to distinguished if they use single quotes   Library code  If you re using a library that uses a particular style  you might consider using the same style yourself  Personal preference  You might think one or other style looks better

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If you use PHP to generate JavaScript code you should use the following declaration  let value    quot  lt  php echo  This is my message   quot double quoted quot  -   single quoted     gt  quot    The output will be  This is my message   quot double quoted quot  -  single quoted   For some reasons it is recommend to use single quotes rather than double quotes in PHP  For the normal behaviour in JavaScript it is recommend to use single quotes   x000D   x000D  var value    This is my message   document getElementById  sample-text   innerHTML   value  x000D   lt span id  sample-text  gt  lt  span gt  x000D   x000D   x000D

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One more thing that you might want to consider as a reason for the shift from double quotes to single quotes is the increase in popularity of server side scripts  When using PHP you can pass variables and parse JavaScript functions using strings and variables in PHP  If you write a string and use double quotes for your PHP you won t have to escape any of the single quotes and PHP will automatically retrieve the value of the variables for you  Example I need to run a JavaScript function using a variable from my server  public static function redirectPage   pageLocation         echo  quot  lt script type  text javascript  gt window location     pageLocation   lt  script gt  quot      This saves me a lot of hassle in having to deal with joining strings  and I can effectively call a JavaScript from PHP  This is only one example  but this may be one of several reasons why programmers are defaulting to single quotes in JavaScript  Quote from PHP documents   The most important feature of double-quoted strings is the fact that variable names will be expanded  See string parsing for details

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I d like to say the difference is purely stylistic  but I m really having my doubts  Consider the following example         Add trim   functionality to JavaScript          1  By extending the String prototype       2  By creating a  stand-alone  function     This is just to demonstrate results are the same in both cases         Extend the String prototype with a trim   method String prototype trim   function         return this replace    s   s   g               Stand-alone  trim   function function trim str        return str replace    s   s   g           document writeln String prototype trim   document writeln trim    In Safari  Chrome  Opera  and Internet Explorer  tested in Internet  Explorer  7 and Internet  Explorer  8   this will return the following  function          return this replace    s   s   g         function trim str        return str replace    s   s   g          However  Firefox will yield a slightly different result  function          return this replace    s   s   g   quot  quot      function trim str        return str replace    s   s   g   quot  quot       The single quotes have been replaced by double quotes   Also note how the indenting space was replaced by four spaces   This gives the impression that at least one browser parses JavaScript internally as if everything was written using double quotes  One might think  it takes Firefox less time to parse JavaScript if everything is already written according to this  standard   Which  by the way  makes me a very sad panda  since I think single quotes look much nicer in code  Plus  in other programming languages  they re usually faster to use than double quotes  so it would only make sense if the same applied to JavaScript  Conclusion  I think we need to do more research on this  This might explain Peter-Paul Koch s test results from back in 2003   It seems that single quotes are sometimes faster in Explorer Windows  roughly 1 3 of my tests did show a faster response time   but if Mozilla shows a difference at all  it handles double quotes slightly faster  I found no difference at all in Opera   2014  Modern versions of Firefox Spidermonkey don   t do this anymore

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There are people that claim to see performance differences  old mailing list thread  But I couldn t find any of them to be confirmed  The main thing is to look at what kind of quotes  double or single  you are using inside your string  It helps to keep the number of escapes low  For instance  when you are working with HTML content inside your strings  it is easier to use single quotes so that you don t have to escape all double quotes around the attributes

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When using CoffeeScript I use double quotes  I agree that you should pick either one and stick to it  CoffeeScript gives you interpolation when using the double quotes   quot This is my   name  quot   ECMAScript  6 is using back ticks     for template strings  Which probably has a good reason  but when coding  it can be cumbersome to change the string literals character from quotes or double quotes to backticks in order to get the interpolation feature  CoffeeScript might not be perfect  but using the same string literals character everywhere  double quotes  and always be able to interpolate is a nice feature   This is my   name

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I think it s important not to forget that while Internet  Explorer might have zero extensions toolbars installed  Firefox might have some extensions installed  I m just thinking of Firebug for instance   Those extensions will have an influence on the benchmark result  Not that it really matters since browser X is faster in getting elementstyles  while browser Y might be faster in rendering a canvas element  hence why a browser  quot manufacturer quot  always has the fastest JavaScript engine

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I think it s important not to forget that while Internet  Explorer might have zero extensions toolbars installed  Firefox might have some extensions installed  I m just thinking of Firebug for instance   Those extensions will have an influence on the benchmark result  Not that it really matters since browser X is faster in getting elementstyles  while browser Y might be faster in rendering a canvas element  hence why a browser  quot manufacturer quot  always has the fastest JavaScript engine

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It s mostly a matter of style and preference  There are some rather interesting and useful technical explorations in the other answers  so perhaps the only thing I might add is to offer a little worldly advice   If you re coding in a company or team  then it s probably a good idea to follow the  quot house style quot    If you re alone hacking a few side projects  then look at a few prominent leaders in the community  For example  let s say you getting into Node js  Take a look at core modules  for example  Underscore js or express and see what convention they use  and consider following that   If both conventions are equally used  then defer to your personal preference   If you don t have any personal preference  then flip a coin   If you don t have a coin  then beer is on me

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If you re jumping back an forth between JavaScript and C   it s best to train your fingers for the common convention which is double quotes

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Strictly speaking  there is no difference in meaning  so the choice comes down to convenience  Here are several factors that could influence your choice   House style  Some groups of developers already use one convention or the other  Client-side requirements  Will you be using quotes within the strings   See Ady s answer   Server-side language  VB NET people might choose to use single quotes for JavaScript so that the scripts can be built server-side  VB NET uses double-quotes for strings  so the JavaScript strings are easy to distinguished if they use single quotes   Library code  If you re using a library that uses a particular style  you might consider using the same style yourself  Personal preference  You might think one or other style looks better

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Technically there s no difference  It s only matter of style and convention  Douglas Crockford recommends using single quotes for internal strings and double quotes for external  by external we mean those to be displayed to user of application  like messages or alerts   I personally follow that  UPDATE  It appears that Mr  Crockford changed his mind and now recommends using double quotes throughout

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It s mostly a matter of style and preference  There are some rather interesting and useful technical explorations in the other answers  so perhaps the only thing I might add is to offer a little worldly advice   If you re coding in a company or team  then it s probably a good idea to follow the  quot house style quot    If you re alone hacking a few side projects  then look at a few prominent leaders in the community  For example  let s say you getting into Node js  Take a look at core modules  for example  Underscore js or express and see what convention they use  and consider following that   If both conventions are equally used  then defer to your personal preference   If you don t have any personal preference  then flip a coin   If you don t have a coin  then beer is on me

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One  silly  reason to use single quotes would be that they don t require you to hit the shift key to type them  whereas a double quote do    I m assuming that the average string doesn t require escaping  which is a reasonable assumption    Now  let s suppose every day I code 200 lines of code   Maybe in those 200 lines I have 30 quotes   Maybe typing a double quote takes 0 1 seconds more time than typing a single quote  because I have to hit the shift key    Then on any given day  I waste 3 seconds   If I code in this manner for 200 days a year for 40 years  then I ve wasted 6 7 hours of my life   Food for thought

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If your JavaScript source is elem innerHTML  quot  lt img src  smily  alt  It  s a Smily  style  width 50px  gt  quot    the HTML source will be   lt img src  quot smiley quot  alt  quot It s a Smiley quot  style  quot width 50px quot  gt   Or for HTML5  lt img src smiley alt  quot It s a Smiley quot  style width 50px gt   JavaScript allows arrays like that  var arr   this   that     But if you stringify it  it will be for compatibility reasons  JSON   quot this quot   quot that quot    I m sure this takes some time

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The most likely reason for use of single vs  double in different libraries is programmer preference and or API consistency  Other than being consistent  use whichever best suits the string  Using the other type of quote as a literal  alert  Say  quot Hello quot     alert  quot Say  Hello  quot     This can get complicated  alert  quot It s   quot game  quot  time  quot    alert  It  s  quot game quot  time      Another option  new in ECMAScript  6  is template literals which use the backtick character  alert  Use  quot double quot  and  single  quotes in the same string    alert  Escape the    back-tick character and the     dollar-brace sequence in a string     Template literals offer a clean syntax for  variable interpolation  multi-line strings  and more  Note that JSON is formally specified to use double quotes  which may be worth considering depending on system requirements

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As stated by other replies  they are almost the same  But I will try to add more   Some efficient algorithms use character arrays to process strings  Those algorithms  browser compiler  etc   would see  quot    34  first before     39  therefore saving several CPU cycles depending on your data structure   quot  is escaped by anti-XSS engines

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If you are using JSHint  it will raise an error if you use a double quoted string  I used it through the Yeoman scafflholding of AngularJS  but maybe there is somehow a manner to configure this  By the way  when you handle HTML into JavaScript  it s easier to use single quote  var foo     lt div class  quot cool-stuff quot  gt Cool content lt  div gt     And at least JSON is using double quotes to represent strings  There isn t any trivial way to answer to your question

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You can use single quotes or double quotes  This enables you for example to easily nest JavaScript content inside HTML attributes  without the need to escape the quotes  The same is when you create JavaScript with PHP  The general idea is  if it is possible use such quotes that you won t need to escape  Less escaping   better code

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Technically there s no difference  It s only matter of style and convention  Douglas Crockford recommends using single quotes for internal strings and double quotes for external  by external we mean those to be displayed to user of application  like messages or alerts   I personally follow that  UPDATE  It appears that Mr  Crockford changed his mind and now recommends using double quotes throughout

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I use single quotes most of the time  because when developing in PHP  single quoted-string are in no way altered  which is what I want  When I use echo  quot  xyz quot    In PHP   xyz gets evaluated  which is not what I want  Therefore I always use   instead of  quot  when it comes to web development  So I ensure at least string-consistency when it comes to PHP JavaScript  Unfortunately this can t be done in Java or Objective-C  where    stands for character and  quot  quot  stands for string  But this is another question

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Personally I prefer single quotes for the sake of readability  If I m staring at code all day it s easier to see the words with just single quotes as opposed to double quotes   Easier to read as demonstrated here    easy to read    harder to read     hardest to read

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I ve been running the following about 20 times  And it appears that double quotes are about 20  faster   The fun part is  if you change part 2 and part 1 around  single quotes are about 20  faster     Part1 var r     var iTime3   new Date   valueOf    for var j 0  j lt 1000000  j          r   a     var iTime4   new Date   valueOf    alert  With single quote        iTime4 - iTime3         Part 2                 var s     var iTime1   new Date   valueOf    for var i 0  i lt 1000000  i          s     a     var iTime2   new Date   valueOf    alert  With double quote       iTime2 - iTime1

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It is just a matter time for me  A few milliseconds lost of my life every time I have to press the Shift key before every time I m able to type  quot   I prefer   simply because you don t have to do it  Other than that  you can escape a   inside single quotes with backslash     console log  Don  t lose time        quot Don t lose time quot

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The difference is purely stylistic  I used to be a double-quote Nazi  Now I use single quotes in nearly all cases  There s no practical difference beyond how your editor highlights the syntax

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There is strictly no difference  so it is mostly a matter of taste and of what is in the string  or if the JavaScript code itself is in a string   to keep number of escapes low  The speed difference legend might come from PHP world  where the two quotes have different behavior

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Let s look what a reference does  Inside jquery js  every string is double-quoted  So  beginning now  I ll use double-quoted strings   I was using single

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I am not sure if this is relevant in today s world  but double quotes used to be used for content that needed to have control characters processed and single quotes for strings that didn t  The compiler will run string manipulation on a double quoted string while leaving a single quoted string literally untouched  This used to lead to  good  developers choosing to use single quotes for strings that didn t contain control characters like  n or  0  not processed within single quotes  and double quotes when they needed the string parsed  at a slight cost in CPU cycles for processing the string

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The difference is purely stylistic  I used to be a double-quote Nazi  Now I use single quotes in nearly all cases  There s no practical difference beyond how your editor highlights the syntax

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If you re dealing with JSON  it should be noted that strictly speaking  JSON strings must be double quoted  Sure  many libraries support single quotes as well  but I had great problems in one of my projects before realizing that single quoting a string is in fact not according to JSON standards

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I hope I am not adding something obvious  but I have been struggling with Django  Ajax  and JSON on this  Assuming that in your HTML code you do use double quotes  as normally should be  I highly suggest to use single quotes for the rest in JavaScript  So I agree with ady  but with some care  My bottom line is  In JavaScript it probably doesn t matter  but as soon as you embed it inside HTML or the like you start to get troubles  You should know what is actually escaping  reading  passing your string  My simple case was  tbox innerHTML   tbox innerHTML     lt div class  quot thisbox des quot  style  quot width 210px  quot  onmouseout  quot clear   quot  gt  lt a href  quot  this thislist                        myThis i  pk    quot  gt  lt img src  quot  site media                        myThis i  fields thumbnail    quot  height  quot 80 quot  width  quot 80 quot  style  quot float left  quot  onmouseover  quot showThis                        myThis i  fields left                           myThis i  fields right                             myThis i  fields title       quot  gt  lt  a gt  lt p style  quot float left width 130px height 80px  quot  gt  lt b gt                        myThis i  fields title    lt  b gt                         myThis i  fields description    lt  p gt  lt  div gt    You can spot the   in the third field of showThis  The double quote didn t work  It is clear why  but it is also clear why we should stick to single quotes    I guess    This case is a very simple HTML embedding  and the error was generated by a simple copy paste from a  double quoted  JavaScript code  So to answer the question  Try to use single quotes while within HTML  It might save a couple of debug issues

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Examining the pros and cons   In favor of single quotes   Less visual clutter  Generating HTML  HTML attributes are usually delimited by double quotes     x000D   x000D  elem innerHTML     lt a href      url      gt Hello lt  a gt    x000D   x000D   x000D   However  single quotes are just as legal in HTML    x000D   x000D  elem innerHTML     lt a href      url      gt Hello lt  a gt    x000D   x000D   x000D    Furthermore  inline HTML is normally an anti-pattern  Prefer templates    Generating JSON  Only double quotes are allowed in JSON     x000D   x000D  myJson       hello world   true     x000D   x000D   x000D    Again  you shouldn   t have to construct JSON this way  JSON stringify   is often enough  If not  use templates   In favor of double quotes   Doubles are easier to spot if you don t have color coding  Like in a console log or some kind of view-source setup  Similarity to other languages  In shell programming  Bash etc    single-quoted string literals exist  but escapes are not interpreted inside them  C and Java use double quotes for strings and single quotes for characters  If you want code to be valid JSON  you need to use double quotes    In favor of both  There is no difference between the two in JavaScript  Therefore  you can use whatever is convenient at the moment  For example  the following string literals all produce the same string    x000D   x000D       He said    Let s go     x000D       He said   Let  s go    x000D       He said    Let  s go     x000D       He said    Let  s go     x000D   x000D   x000D    Single quotes for internal strings and double for external  That allows you to distinguish internal constants from strings that are to be displayed to the user  or written to disk etc    Obviously  you should avoid putting the latter in your code  but that can   t always be done

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Just keep consistency in what you use  But don t let down your comfort level   quot This is my string  quot       -   quot I m invincible  quot      Comfortable     You can  t beat me       Uncomfortable     Oh  Yes  I can  quot beat quot  you       Comfortable     quot Do you really think  you can   quot beat  quot  me  quot      Uncomfortable     quot You re my guest  I can   quot beat  quot  you  quot      Sometimes  you ve to  P  You  re my guest too  I can  quot beat quot  you too       Sometimes  you ve to  P  ECMAScript  6 update Using template literal syntax   Be  quot my quot  guest  You re in complete freedom       Most comfort  D

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There are people that claim to see performance differences  old mailing list thread  But I couldn t find any of them to be confirmed  The main thing is to look at what kind of quotes  double or single  you are using inside your string  It helps to keep the number of escapes low  For instance  when you are working with HTML content inside your strings  it is easier to use single quotes so that you don t have to escape all double quotes around the attributes

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After reading all the answers that say it may be be faster or may be have advantages  I would say double quotes are better or may be faster too because the Google Closure compiler converts single quotes to double quotes

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I ve been running the following about 20 times  And it appears that double quotes are about 20  faster   The fun part is  if you change part 2 and part 1 around  single quotes are about 20  faster     Part1 var r     var iTime3   new Date   valueOf    for var j 0  j lt 1000000  j          r   a     var iTime4   new Date   valueOf    alert  With single quote        iTime4 - iTime3         Part 2                 var s     var iTime1   new Date   valueOf    for var i 0  i lt 1000000  i          s     a     var iTime2   new Date   valueOf    alert  With double quote       iTime2 - iTime1

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For me  if I code in a Vim editor and if something is enclosed in single quotes  I can double-click to select only the text within the quotes  Double quotes  on the other hand  include the quote marks which I find annoying when I want to do some quick copy and pasting  E g   myVar  double-click in the Vim editor copies   gt myVar lt   quot myVar quot  literally copies   gt  quot myVar quot  lt  and when I paste  I have to delete the quote marks on either side

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Strictly speaking  there is no difference in meaning  so the choice comes down to convenience  Here are several factors that could influence your choice   House style  Some groups of developers already use one convention or the other  Client-side requirements  Will you be using quotes within the strings   See Ady s answer   Server-side language  VB NET people might choose to use single quotes for JavaScript so that the scripts can be built server-side  VB NET uses double-quotes for strings  so the JavaScript strings are easy to distinguished if they use single quotes   Library code  If you re using a library that uses a particular style  you might consider using the same style yourself  Personal preference  You might think one or other style looks better

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If your JavaScript source is elem innerHTML  quot  lt img src  smily  alt  It  s a Smily  style  width 50px  gt  quot    the HTML source will be   lt img src  quot smiley quot  alt  quot It s a Smiley quot  style  quot width 50px quot  gt   Or for HTML5  lt img src smiley alt  quot It s a Smiley quot  style width 50px gt   JavaScript allows arrays like that  var arr   this   that     But if you stringify it  it will be for compatibility reasons  JSON   quot this quot   quot that quot    I m sure this takes some time

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There is no one better solution  however  I would like to argue that double quotes may be more desirable at times    Newcomers will already be familiar with double quotes from their language   In English  we must use double quotes   to identify a passage of quoted text   If we were to use a single quote    the reader may misinterpret it as a contraction   The other meaning of a passage of text surrounded by the   indicates the  colloquial  meaning   It makes sense to stay consistent with pre-existing languages  and this may likely ease the learning and interpretation of code  Double quotes eliminate the need to escape apostrophes  as in contractions    Consider the string   I m going to the mall   vs  the otherwise escaped version   I  m going to the mall   Double quotes mean a string in many other languages   When you learn a new language like Java or C  double quotes are always used  In Ruby  PHP and Perl  single-quoted strings imply no backslash escapes while double quotes support them    JSON notation is written with double quotes    Nonetheless  as others have stated  it is most important to remain consistent

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There are people that claim to see performance differences  old mailing list thread  But I couldn t find any of them to be confirmed  The main thing is to look at what kind of quotes  double or single  you are using inside your string  It helps to keep the number of escapes low  For instance  when you are working with HTML content inside your strings  it is easier to use single quotes so that you don t have to escape all double quotes around the attributes

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Just to add my two cents  In working with both JavaScript and PHP a few years back  I ve become accustomed to using single quotes so I can type the escape character      without having to escape it as well  I usually used it when typing raw strings with file paths  etc  Anyhow  my convention ended up becoming the use of single quotes on identifier-type raw strings  such as if  typeof s     string        in which escape characters would never be used - ever   and double quotes for texts  such as  quot Hey  what s up  quot    I also use single quotes in comments as a typographical convention to show identifier names  This is just a rule of thumb  and I break off only when needed  such as when typing HTML strings   lt a href  quot   quot  gt  like so  lt a gt    though you could reverse the quotes here also   I m also aware that  in the case of JSON  double quotes are used for the names - but outside that  personally  I prefer the single quotes when escaping is never required for the text between the quotes - like document createElement  div    The bottom line is  and as some have mentioned alluded to  to pick a convention  stick with it  and only deviate when necessary

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Let s look what a reference does  Inside jquery js  every string is double-quoted  So  beginning now  I ll use double-quoted strings   I was using single

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I use single quotes most of the time  because when developing in PHP  single quoted-string are in no way altered  which is what I want  When I use echo  quot  xyz quot    In PHP   xyz gets evaluated  which is not what I want  Therefore I always use   instead of  quot  when it comes to web development  So I ensure at least string-consistency when it comes to PHP JavaScript  Unfortunately this can t be done in Java or Objective-C  where    stands for character and  quot  quot  stands for string  But this is another question

[javascript] When should I use double or single quotes in JavaScript?

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