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gdoron
gdoron

Reputation: 150253

Casting to string in JavaScript

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?

Upvotes: 242

Views: 467263

Answers (9)

ben
ben

Reputation: 497

Use Backticks

so:

`${varibale}`

Upvotes: 0

Simone C.
Simone C.

Reputation: 191

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

Upvotes: 15

jldec
jldec

Reputation: 99

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.

Upvotes: 9

Jack
Jack

Reputation: 1911

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.

Upvotes: 6

Sarfraz
Sarfraz

Reputation: 382696

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"

Upvotes: 21

itinance
itinance

Reputation: 12388

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

Upvotes: 0

Connell
Connell

Reputation: 14411

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.

Upvotes: 289

jbabey
jbabey

Reputation: 46647

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/

Upvotes: 38

Sammy S.
Sammy S.

Reputation: 1290

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.

Upvotes: 10

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