What is the correct way to check for string equality in JavaScript

Question

What is the correct way to check for equality between Strings in JavaScript

User · Answer

There are actually two ways in which strings can be made in javascript.

var str = 'Javascript'; This creates a primitive string value.
var obj = new String('Javascript'); This creates a wrapper object of type String.

typeof str // string
typeof obj // object

So the best way to check for equality is using the === operator because it checks value as well as type of both operands.

If you want to check for equality between two objects then using String.prototype.valueOf is the correct way.

new String('javascript').valueOf() == new String('javascript').valueOf()

User · Answer

what led me to this question is the padding and white-spaces    check my case   if  title      LastName         doSomething      and title was             LastName        so maybe you have to use trim function like this   var title     this  text   trim

User · Answer

You can use    or     but last one works in more simple way  src  a    b  and its negation      a     b  and its negation

User · Answer

Considering that both strings may be very large  there are 2 main approaches bitwise search and localeCompare  I recommed this function  function compareLargeStrings a b       if  a length     b length             return false            return a localeCompare b      0

User · Answer

Just one addition to answers  If all these methods return false  even if strings seem to be equal  it is possible that there is a whitespace to the left and or right of one string  So  just put a  trim   at the end of strings before comparing   if s1 trim       s2 trim             your code     I have lost hours trying to figure out what is wrong  Hope this will help to someone

User · Answer

If you know they are strings  then there s no need to check for type    a      b    However  note that string objects will not be equal   new String  a      new String  a     will return false   Call the valueOf   method to convert it to a primitive for String objects   new String  a   valueOf      new String  a   valueOf     will return true

User · Answer

String Objects can be checked using JSON stringify   trick   x000D   x000D  var me   new String  me    var you   new String  me    var isEquel   JSON stringify me      JSON stringify you   console log isEquel   x000D   x000D   x000D

User · Answer

always Until you fully understand the differences and implications of using the    and     operators  use the     operator since it will save you from obscure  non-obvious  bugs and WTFs   The  regular     operator can have very unexpected results due to the type-coercion internally  so using     is always the recommended approach   For insight into this  and other  good vs  bad  parts of Javascript read up on Mr  Douglas Crockford and his work   There s a great Google Tech Talk where he summarizes lots of good info  http   www youtube com watch v hQVTIJBZook    Update   The You Don t Know JS series by Kyle Simpson is excellent  and free to read online    The series goes into the commonly misunderstood areas of the language and explains the  bad parts  that Crockford suggests you avoid   By understanding them you can make proper use of them and avoid the pitfalls   The  Up  amp  Going  book includes a section on Equality  with this specific summary of when to use the loose      vs strict       operators      To boil down a whole lot of details to a few simple takeaways  and help you know whether to use    or     in various situations  here are my simple rules          If either value  aka side  in a comparison could be the true or false value  avoid    and use        If either value in a comparison could be of these specific values  0      or    -- empty array   avoid    and use        In all other cases  you re safe to use     Not only is it safe  but in many cases it simplifies your code in a way that improves readability       I still recommend Crockford s talk for developers who don t want to invest the time to really understand Javascript mdash it s good advice for a developer who only occasionally works in Javascript

[javascript] What is the correct way to check for string equality in JavaScript?

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