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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:
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 |