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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.

Try it

Syntax

Symbol()
Symbol(description)

Note: Symbol() can only be called without new. Attempting to construct it with new throws a TypeError.

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:

const sym1 = Symbol();
const sym2 = Symbol('foo');
const 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:

const 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:

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

Specifications

Browser compatibility

Desktop Mobile Server
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet Deno Node.js
Symbol
38
12
36
No
25
9
38
38
36
25
9
3.0
1.0
0.12.0

See also

© 2005–2022 MDN contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/Symbol