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Symbol.symbol

The Symbol() constructor returns a value of type symbol, but is incomplete as a constructor because it does not support the syntax "new Symbol()" and it is not intended to be subclassed. It may be used as the value of an extends clause of a class definition but a super call to it will cause an exception.

Syntax

Symbol([description])

Parameters

description Optional
A string. A description of the symbol which can be used for debugging but not to access the symbol itself.

Examples

Creating symbols

To create a new primitive symbol, you write Symbol() with an optional string as its description:

let sym1 = Symbol()
let sym2 = Symbol('foo')
let sym3 = Symbol('foo')

The above code creates three new symbols. Note that Symbol("foo") does not coerce the string "foo" into a symbol. It creates a new symbol each time:

Symbol('foo') === Symbol('foo')  // false

new Symbol(...)

The following syntax with the new operator will throw a TypeError:

let sym = new Symbol()  // TypeError

This prevents authors from creating an explicit Symbol wrapper object instead of a new symbol value and might be surprising as creating explicit wrapper objects around primitive data types is generally possible (for example, new Boolean, new String and new Number).

If you really want to create a Symbol wrapper object, you can use the Object() function:

let sym    = Symbol('foo');
let symObj = Object(sym);
typeof sym    // => "symbol" 
typeof symObj // => "object"

Specifications

Browser compatibilityUpdate compatibility data on GitHub

Desktop
Chrome Edge Firefox Internet Explorer Opera Safari
Symbol() constructor 38 12 36 No 25 9
Mobile
Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet
Symbol() constructor 38 38 36 25 9 3.0
Server
Node.js
Symbol() constructor 0.12

See also

© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://wiki.developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/Symbol