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.
Symbol([description])
description
Optional
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
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"
Desktop | ||||||
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Symbol() constructor |
38 | 12 | 36 | No | 25 | 9 |
Mobile | ||||||
---|---|---|---|---|---|---|
Symbol() constructor |
38 | 38 | 36 | 25 | 9 | 3.0 |
Server | |
---|---|
Symbol() constructor |
0.12 |
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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