Why would a JavaScript variable start with a dollar sign

Question

I quite often see JavaScript with variables that start with a dollar sign  When why would you choose to prefix a variable in this way    I m not asking about    p foo   syntax that you see in jQuery and others  but normal variables like  name and  order

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varname  is just a naming convention jQuery developers use to distinguish variables that are holding jQuery elements   Plain  varname  is used to store general stuffs like texts and strings    varname  holds elements returned from jQuery   You can use plain  varname  to store jQuery elements as well  but as I said in the beginning this distinguishes it from the plain variables and makes it much easier to understand  imagine confusing it for a plain variable and searching all over to understand what it holds     For example    var  blah     this  parents   blahblah      Here  blah is storing a returned jQuery element   So  when someone else see the  blah in the code  they ll understand it s not just a string or a number  it s a jQuery element

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Angular uses is for properties generated by the framework  Guess  they are going by the  now defunct  hint provided by the ECMA-262 3 0

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The   character has no special meaning to the JavaScript engine   It s just another valid character in a variable name like a-z  A-Z     0-9  etc

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As others have mentioned the dollar sign is intended to be used by mechanically generated code   However  that convention has been broken by some wildly popular JavaScript libraries   JQuery  Prototype and MS AJAX  AKA Atlas  all use this character in their identifiers  or as an entire identifier    In short you can use the   whenever you want    The interpreter won t complain    The question is when do you want to use it   I personally do not use it  but I think its use is valid   I think MS AJAX uses it to signify that a function is an alias for some more verbose call   For example   var  get   function id    return document getElementById id       That seems like a reasonable convention

User · Answer

In the 1st  2nd  and 3rd Edition of ECMAScript  using  -prefixed variable names was explicitly discouraged by the spec except in the context of autogenerated code      The dollar sign     and the underscore     are permitted anywhere in an identifier  The dollar sign is intended for use only in mechanically generated code    However  in the next version  the 5th Edition  which is current   this restriction was dropped  and the above passage replaced with     The dollar sign     and the underscore     are permitted anywhere in an IdentifierName    As such  the   sign may now be used freely in variable names  Certain frameworks and libraries have their own conventions on the meaning of the symbol  noted in other answers here

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While you can simply use it to prefix your identifiers  it s supposed to be used for generated code  such as replacement tokens in a template  for example

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The reason I sometimes use php name-conventions with javascript variables  When doing input validation  I want to run the exact same algorithms both client-side  and server-side   I really want the two side of code to look as similar as possible  to simplify maintenance   Using dollar signs in variable names makes this easier    Also  some judicious helper functions help make the code look similar  e g  wrapping input-value-lookups  non-OO versions of strlen substr  etc   It still requires some manual tweaking though

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Since   at the beginning of a variable name is often used to indicate a private variable  or at least one intended to remain private   I find   convenient for adding in front of my own brief aliases to generic code libraries   For example  when using jQuery  I prefer to use the variable  J  instead of just    and use  P when using php js  etc   The prefix makes it visually distinct from other variables such as my own static variables  cluing me into the fact that the code is part of some library or other  and is less likely to conflict or confuse others once they know the convention   It also doesn t clutter the code  or require extra typing  as does a fully specified name repeated for each library call   I like to think of it as being similar to what modifier keys do for expanding the possibilities of single keys   But this is just my own convention

User · Answer

While you can simply use it to prefix your identifiers  it s supposed to be used for generated code  such as replacement tokens in a template  for example

User · Answer

Very common use in jQuery is to distinguish jQuery objects stored in variables from other variables     For example  I would define   var  email       email       refers to the jQuery object representation of the dom object var email field       email   get 0      refers to the dom object itself   I find this to be very helpful in writing jQuery code and makes it easy to see jQuery objects which have a different set of properties

User · Answer

Since   at the beginning of a variable name is often used to indicate a private variable  or at least one intended to remain private   I find   convenient for adding in front of my own brief aliases to generic code libraries   For example  when using jQuery  I prefer to use the variable  J  instead of just    and use  P when using php js  etc   The prefix makes it visually distinct from other variables such as my own static variables  cluing me into the fact that the code is part of some library or other  and is less likely to conflict or confuse others once they know the convention   It also doesn t clutter the code  or require extra typing  as does a fully specified name repeated for each library call   I like to think of it as being similar to what modifier keys do for expanding the possibilities of single keys   But this is just my own convention

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In the context of AngularJS  the   prefix is used only for identifiers in the framework s code  Users of the framework are instructed not to use it in their own identifiers      Angular Namespaces   and         To prevent accidental name collisions with your code  Angular prefixes names of public objects with   and names of private objects with     Please do not use the   or    prefix in your code    Source  https   docs angularjs org api

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If you see the dollar sign     or double dollar sign       and are curious as to what this means in the Prototype framework  here is your answer       div       - gt  all DIVs in the document   Same as document getElementsByTagName  div          contents       - gt  same as    contents    only it returns an array anyway  even though IDs must be unique within a document        li faux       - gt  all LI elements with class  faux    Source  http   www prototypejs org api utility dollar-dollar

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Stevo is right  the meaning and usage of the dollar script sign  in Javascript and the jQuery platform  but not in PHP  is completely semantic    is a character that can be used as part of an identifier name  In addition  the dollar sign is perhaps not the most  weird  thing you can encounter in Javascript  Here are some examples of valid identifier names   var           function     alert  hello from        var  u0024    function     alert  hello from   defined as u0024      var            function     alert  hello from         var           function     alert  hello from              All of the examples above will work   Try them

User · Answer

While you can simply use it to prefix your identifiers  it s supposed to be used for generated code  such as replacement tokens in a template  for example

User · Answer

In the context of AngularJS  the   prefix is used only for identifiers in the framework s code  Users of the framework are instructed not to use it in their own identifiers      Angular Namespaces   and         To prevent accidental name collisions with your code  Angular prefixes names of public objects with   and names of private objects with     Please do not use the   or    prefix in your code    Source  https   docs angularjs org api

User · Answer

Stevo is right  the meaning and usage of the dollar script sign  in Javascript and the jQuery platform  but not in PHP  is completely semantic    is a character that can be used as part of an identifier name  In addition  the dollar sign is perhaps not the most  weird  thing you can encounter in Javascript  Here are some examples of valid identifier names   var           function     alert  hello from        var  u0024    function     alert  hello from   defined as u0024      var            function     alert  hello from         var           function     alert  hello from              All of the examples above will work   Try them

User · Answer

Angular uses is for properties generated by the framework  Guess  they are going by the  now defunct  hint provided by the ECMA-262 3 0

User · Answer

In the 1st  2nd  and 3rd Edition of ECMAScript  using  -prefixed variable names was explicitly discouraged by the spec except in the context of autogenerated code      The dollar sign     and the underscore     are permitted anywhere in an identifier  The dollar sign is intended for use only in mechanically generated code    However  in the next version  the 5th Edition  which is current   this restriction was dropped  and the above passage replaced with     The dollar sign     and the underscore     are permitted anywhere in an IdentifierName    As such  the   sign may now be used freely in variable names  Certain frameworks and libraries have their own conventions on the meaning of the symbol  noted in other answers here

User · Answer

While you can simply use it to prefix your identifiers  it s supposed to be used for generated code  such as replacement tokens in a template  for example

User · Answer

is used to DISTINGUISH between common variables and jquery variables in case of normal variables  let you place a order in FLIPKART then if the order is a variable showing you the string output then it is named simple as  order  but if we click on place order then an object is returned that object will be denoted by   as   order  so that the programmer may able to snip out the javascript variables and jquery variables in the entire code

User · Answer

The   character has no special meaning to the JavaScript engine   It s just another valid character in a variable name like a-z  A-Z     0-9  etc

User · Answer

As others have mentioned the dollar sign is intended to be used by mechanically generated code   However  that convention has been broken by some wildly popular JavaScript libraries   JQuery  Prototype and MS AJAX  AKA Atlas  all use this character in their identifiers  or as an entire identifier    In short you can use the   whenever you want    The interpreter won t complain    The question is when do you want to use it   I personally do not use it  but I think its use is valid   I think MS AJAX uses it to signify that a function is an alias for some more verbose call   For example   var  get   function id    return document getElementById id       That seems like a reasonable convention

User · Answer

A valid JavaScript identifier shuold must start with a letter      underscore      or dollar sign          subsequent characters can also     be digits  0-9   Because JavaScript is case sensitive       letters     include the characters  A  through  Z   uppercase  and the     characters  a  through  z   lowercase    Details  https   developer mozilla org en-US docs Web JavaScript Guide Grammar and types Variables

User · Answer

Very common use in jQuery is to distinguish jQuery objects stored in variables from other variables     For example  I would define   var  email       email       refers to the jQuery object representation of the dom object var email field       email   get 0      refers to the dom object itself   I find this to be very helpful in writing jQuery code and makes it easy to see jQuery objects which have a different set of properties

User · Answer

The reason I sometimes use php name-conventions with javascript variables  When doing input validation  I want to run the exact same algorithms both client-side  and server-side   I really want the two side of code to look as similar as possible  to simplify maintenance   Using dollar signs in variable names makes this easier    Also  some judicious helper functions help make the code look similar  e g  wrapping input-value-lookups  non-OO versions of strlen substr  etc   It still requires some manual tweaking though

User · Answer

I was the person who originated this convention back in 2006 and promoted it on the early jQuery mailing list  so let me share some of the history and motivation around it   The accepted answer gives this example   var  email       email       refers to the jQuery object representation of the dom object var email field       email   get 0      refers to the dom object itself   But that doesn t really illustrate it well  Even without the    we would still have two different variable names here  email and email field  That s plenty good right there  Why would we need to throw a   into one of the names when we already have two different names   Actually  I wouldn t have used email field here for two reasons  names with underscores are not idiomatic JavaScript  and field doesn t really make sense for a DOM element  But I did follow the same idea   I tried a few different things  among them something very similar to the example   var email       email    emailElement       email   0      Now email is a jQuery object and emailElement is the first only DOM element in it    Of course a jQuery object can have more than one DOM element  but the code I was working on had a lot of id selectors  so in those cases there was a 1 1 correspondence    I had another case where a function received a DOM element as a parameter and also needed a jQuery object for it      email is a DOM element passed into this function function doSomethingWithEmail  email         var emailJQ     email          Now email is the DOM element and emailJQ is a jQuery object for it     Well that s a little confusing  In one of my bits of code  email is the jQuery object and emailElement is the DOM element  but in the other  email is the DOM element and emailJQ is the jQuery object   There was no consistency and I kept mixing them up  Plus it was a bit of a nuisance to keep having to make up two different names for the same thing  one for the jQuery object and another for the matching DOM element  Besides email  emailElement  and emailJQ  I kept trying other variations too   Then I noticed a common pattern   var email       email    var emailJQ     email     Since JavaScript treats   as simply another letter for names  and since I always got a jQuery object back from a   whatever  call  the pattern finally dawned on me  I could take a        call and just remove some characters  and it would come up with a pretty nice name        email     email    Strikeout isn t perfect  but you may get the idea  with some characters deleted  both of those lines end up looking like    email   That s when I realized I didn t need to make up a convention like emailElement or emailJQ  There was already a nice convention staring at me  take some characters out of a   whatever  call and it turns into  whatever   var  email       email    email    email 0       email is the jQuery object and email is the DOM object   and      email is a DOM element passed into this function function doSomethingWithEmail  email         var  email     email           email is the jQuery object and email is the DOM object        Same names as in the code above  Yay      So I didn t have to make up two different names all the time but could just use the same name with or without a   prefix  And the   prefix was a nice reminder that I was dealing with a jQuery object       email   click           or   var  email       email       Maybe do some other stuff with  email here  email click

User · Answer

In the 1st  2nd  and 3rd Edition of ECMAScript  using  -prefixed variable names was explicitly discouraged by the spec except in the context of autogenerated code      The dollar sign     and the underscore     are permitted anywhere in an identifier  The dollar sign is intended for use only in mechanically generated code    However  in the next version  the 5th Edition  which is current   this restriction was dropped  and the above passage replaced with     The dollar sign     and the underscore     are permitted anywhere in an IdentifierName    As such  the   sign may now be used freely in variable names  Certain frameworks and libraries have their own conventions on the meaning of the symbol  noted in other answers here

User · Answer

As others have mentioned the dollar sign is intended to be used by mechanically generated code   However  that convention has been broken by some wildly popular JavaScript libraries   JQuery  Prototype and MS AJAX  AKA Atlas  all use this character in their identifiers  or as an entire identifier    In short you can use the   whenever you want    The interpreter won t complain    The question is when do you want to use it   I personally do not use it  but I think its use is valid   I think MS AJAX uses it to signify that a function is an alias for some more verbose call   For example   var  get   function id    return document getElementById id       That seems like a reasonable convention

User · Answer

A valid JavaScript identifier shuold must start with a letter      underscore      or dollar sign          subsequent characters can also     be digits  0-9   Because JavaScript is case sensitive       letters     include the characters  A  through  Z   uppercase  and the     characters  a  through  z   lowercase    Details  https   developer mozilla org en-US docs Web JavaScript Guide Grammar and types Variables

User · Answer

varname  is just a naming convention jQuery developers use to distinguish variables that are holding jQuery elements   Plain  varname  is used to store general stuffs like texts and strings    varname  holds elements returned from jQuery   You can use plain  varname  to store jQuery elements as well  but as I said in the beginning this distinguishes it from the plain variables and makes it much easier to understand  imagine confusing it for a plain variable and searching all over to understand what it holds     For example    var  blah     this  parents   blahblah      Here  blah is storing a returned jQuery element   So  when someone else see the  blah in the code  they ll understand it s not just a string or a number  it s a jQuery element

User · Answer

As others have mentioned the dollar sign is intended to be used by mechanically generated code   However  that convention has been broken by some wildly popular JavaScript libraries   JQuery  Prototype and MS AJAX  AKA Atlas  all use this character in their identifiers  or as an entire identifier    In short you can use the   whenever you want    The interpreter won t complain    The question is when do you want to use it   I personally do not use it  but I think its use is valid   I think MS AJAX uses it to signify that a function is an alias for some more verbose call   For example   var  get   function id    return document getElementById id       That seems like a reasonable convention

User · Answer

As I have experienced for the last 4 years  it will allow some one to easily identify whether the variable pointing  a value object or a jQuery wrapped DOM element   x000D   x000D  Ex  x000D  var name    jQuery   x000D  var lib    name  jQuery  version 1 6   x000D   x000D  var  dataDiv       myDataDiv    x000D   x000D   x000D    in the above example when I see the variable   dataDiv  i can easily say that this variable pointing to a jQuery wrapped DOM element  in this case it is div   and also I can call all the jQuery methods with out wrapping the object again like  dataDiv append     dataDiv html     dataDiv find   instead of    dataDiv  append     Hope it may helped  so finally want to say that it will be a good practice to follow this but not mandatory

User · Answer

I was the person who originated this convention back in 2006 and promoted it on the early jQuery mailing list  so let me share some of the history and motivation around it   The accepted answer gives this example   var  email       email       refers to the jQuery object representation of the dom object var email field       email   get 0      refers to the dom object itself   But that doesn t really illustrate it well  Even without the    we would still have two different variable names here  email and email field  That s plenty good right there  Why would we need to throw a   into one of the names when we already have two different names   Actually  I wouldn t have used email field here for two reasons  names with underscores are not idiomatic JavaScript  and field doesn t really make sense for a DOM element  But I did follow the same idea   I tried a few different things  among them something very similar to the example   var email       email    emailElement       email   0      Now email is a jQuery object and emailElement is the first only DOM element in it    Of course a jQuery object can have more than one DOM element  but the code I was working on had a lot of id selectors  so in those cases there was a 1 1 correspondence    I had another case where a function received a DOM element as a parameter and also needed a jQuery object for it      email is a DOM element passed into this function function doSomethingWithEmail  email         var emailJQ     email          Now email is the DOM element and emailJQ is a jQuery object for it     Well that s a little confusing  In one of my bits of code  email is the jQuery object and emailElement is the DOM element  but in the other  email is the DOM element and emailJQ is the jQuery object   There was no consistency and I kept mixing them up  Plus it was a bit of a nuisance to keep having to make up two different names for the same thing  one for the jQuery object and another for the matching DOM element  Besides email  emailElement  and emailJQ  I kept trying other variations too   Then I noticed a common pattern   var email       email    var emailJQ     email     Since JavaScript treats   as simply another letter for names  and since I always got a jQuery object back from a   whatever  call  the pattern finally dawned on me  I could take a        call and just remove some characters  and it would come up with a pretty nice name        email     email    Strikeout isn t perfect  but you may get the idea  with some characters deleted  both of those lines end up looking like    email   That s when I realized I didn t need to make up a convention like emailElement or emailJQ  There was already a nice convention staring at me  take some characters out of a   whatever  call and it turns into  whatever   var  email       email    email    email 0       email is the jQuery object and email is the DOM object   and      email is a DOM element passed into this function function doSomethingWithEmail  email         var  email     email           email is the jQuery object and email is the DOM object        Same names as in the code above  Yay      So I didn t have to make up two different names all the time but could just use the same name with or without a   prefix  And the   prefix was a nice reminder that I was dealing with a jQuery object       email   click           or   var  email       email       Maybe do some other stuff with  email here  email click

User · Answer

If you see the dollar sign     or double dollar sign       and are curious as to what this means in the Prototype framework  here is your answer       div       - gt  all DIVs in the document   Same as document getElementsByTagName  div          contents       - gt  same as    contents    only it returns an array anyway  even though IDs must be unique within a document        li faux       - gt  all LI elements with class  faux    Source  http   www prototypejs org api utility dollar-dollar

User · Answer

As I have experienced for the last 4 years  it will allow some one to easily identify whether the variable pointing  a value object or a jQuery wrapped DOM element   x000D   x000D  Ex  x000D  var name    jQuery   x000D  var lib    name  jQuery  version 1 6   x000D   x000D  var  dataDiv       myDataDiv    x000D   x000D   x000D    in the above example when I see the variable   dataDiv  i can easily say that this variable pointing to a jQuery wrapped DOM element  in this case it is div   and also I can call all the jQuery methods with out wrapping the object again like  dataDiv append     dataDiv html     dataDiv find   instead of    dataDiv  append     Hope it may helped  so finally want to say that it will be a good practice to follow this but not mandatory

User · Answer

In the 1st  2nd  and 3rd Edition of ECMAScript  using  -prefixed variable names was explicitly discouraged by the spec except in the context of autogenerated code      The dollar sign     and the underscore     are permitted anywhere in an identifier  The dollar sign is intended for use only in mechanically generated code    However  in the next version  the 5th Edition  which is current   this restriction was dropped  and the above passage replaced with     The dollar sign     and the underscore     are permitted anywhere in an IdentifierName    As such  the   sign may now be used freely in variable names  Certain frameworks and libraries have their own conventions on the meaning of the symbol  noted in other answers here

User · Answer

is used to DISTINGUISH between common variables and jquery variables in case of normal variables  let you place a order in FLIPKART then if the order is a variable showing you the string output then it is named simple as  order  but if we click on place order then an object is returned that object will be denoted by   as   order  so that the programmer may able to snip out the javascript variables and jquery variables in the entire code

[javascript] Why would a JavaScript variable start with a dollar sign?

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