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
Specification |
---|
ECMAScript (ECMA-262) The definition of 'Symbol constructor' in that specification. |
Browser compatibility
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Symbol() constructor | Chrome Full support 38 | Edge Full support 12 | Firefox Full support 36 | IE No support No | Opera Full support 25 | Safari Full support 9 | WebView Android Full support 38 | Chrome Android Full support 38 | Firefox Android Full support 36 | Opera Android Full support 25 | Safari iOS Full support 9 | Samsung Internet Android Full support 3.0 | nodejs Full support 0.12 |
Legend
- Full support
- Full support
- No support
- No support