Symbol.for()

The Symbol.for(key) method searches for existing symbols in a runtime-wide symbol registry with the given key and returns it if found. Otherwise a new symbol gets created in the global symbol registry with this key.

Syntax

Symbol.for(key);

Parameters

key
String, required. The key for the symbol (and also used for the description of the symbol).

Return value

An existing symbol with the given key if found; otherwise, a new symbol is created and returned.

Description

In contrast to Symbol(), the Symbol.for() function creates a symbol available in a global symbol registry list. Symbol.for() does also not necessarily create a new symbol on every call, but checks first if a symbol with the given key is already present in the registry. In that case, that symbol is returned. If no symbol with the given key is found, Symbol.for() will create a new global symbol.

Global symbol registry

The global symbol registry is a list with the following record structure and it is initialized empty:

A record in the global symbol registry
Field name Value
[[key]] A string key used to identify a symbol.
[[symbol]] A symbol that is stored globally.

Examples

Symbol.for("foo"); // create a new global symbol
Symbol.for("foo"); // retrieve the already created symbol

// Same global symbol, but not locally
Symbol.for("bar") === Symbol.for("bar"); // true
Symbol("bar") === Symbol("bar"); // false

// The key is also used as the description
var sym = Symbol.for("mario");
sym.toString(); // "Symbol(mario)"

To avoid name clashes with your global symbol keys and other (library code) global symbols, it might be a good idea to prefix your symbols:

Symbol.for("mdn.foo");
Symbol.for("mdn.bar");

Specifications

Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'Symbol.for' in that specification.
Standard Initial definition.
ECMAScript 2017 Draft (ECMA-262)
The definition of 'Symbol.for' in that specification.
Draft  

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support 40 36.0 (36.0) No support No support No support
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support No support No support 36.0 (36.0) No support No support No support

See also

Document Tags and Contributors

 Contributors to this page: eduardoboucas, fscholz, Hixhi, steelbrain
 Last updated by: eduardoboucas,