Symbol() constructor
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()
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 Language Specification # sec-symbol-constructor |
Browser compatibility
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