Casting to string in JavaScript

Question

I found three ways to cast a variable to String in JavaScript  I searched for those three options in the jQuery source code  and they are all in use  I would like to know if there are any differences between them   value toString   String value  value        DEMO  They all produce the same output  but does one of them better than the others  I would say the      has an advantage that it saves some characters  but that s not that big advantage  anything else

User · Answer

There are differences  but they are probably not relevant to your question  For example  the toString prototype does not exist on undefined variables  but you can cast undefined to a string using the other two methods    var foo    var myString1   String foo       undefined  as a string  var myString2   foo           undefined  as a string  var myString3   foo toString       throws an exception   http   jsfiddle net f8YwA

User · Answer

On this page you can test the performance of each method yourself     http   jsperf com cast-to-string 2  here  on all machines and browsers         str   is the fastest one   String str is the slowest

User · Answer

In addition to all the above  one should note that  for a defined value v    String v  calls v toString        v calls v valueOf   prior to any other type cast   So we could do something like   var mixin       valueOf   function      return false      toString  function      return  true       mixin     false      false mixin    false        true      mixin            false  String mixin          true    Tested in FF 34 0 and Node 0 10

User · Answer

According to this JSPerf test  they differ in speed  But unless you re going to use them in huge amounts  any of them should perform fine   For completeness  As asawyer already mentioned  you can also use the  toString   method

User · Answer

if you are ok with null  undefined  NaN  0  and false all casting to    then  s   s          is faster   see http   jsperf com cast-to-string 8  note - there are significant differences across browsers at this time

User · Answer

They do behave differently when the value is null    null toString   throws an error - Cannot call method  toString  of null String null  returns -  null  null      also returns -  null    Very similar behaviour happens if value is undefined  see jbabey s answer    Other than that  there is a negligible performance difference  which  unless you re using them in huge loops  isn t worth worrying about

User · Answer

They behave the same but toString also provides a way to convert a number binary  octal  or hexadecimal strings   Example   var a    50274  toString 16       c462  var b    76  toString 8           114  var c    7623  toString 36        5vr  var d    100  toString 2          1100100

User · Answer

Real world example  I ve got a log function that can be called with an arbitrary number of parameters  log  foo is    and bar is      param1  param2   If a DEBUG flag is set to true  the brackets get replaced by the given parameters and the string is passed to console log msg   Parameters can and will be Strings  Numbers and whatever may be returned by JSON   AJAX calls  maybe even null    arguments i  toString   is not an option  because of possible null values  see Connell Watkins answer  JSLint will complain about arguments i        This may or may not influence a decision on what to use  Some folks strictly adhere to JSLint  In some browsers  concatenating empty strings is a little faster than using string function or string constructor  see JSPerf test in Sammys S  answer   In Opera 12 and Firefox 19  concatenating empty strings is rediculously faster  95  in Firefox 19  - or at least JSPerf says so

[javascript] Casting to string in JavaScript

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