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.
The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.
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
Using Symbol.for
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 |
---|
ECMAScript (ECMA-262) The definition of 'Symbol.for' in that specification. |
Browser compatibility
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
for | Chrome Full support 40 | Edge Full support 12 | Firefox Full support 36 | IE No support No | Opera Full support 27 | Safari Full support 9 | WebView Android Full support 40 | Chrome Android Full support 40 | Firefox Android Full support 36 | Opera Android Full support 27 | Safari iOS Full support 9 | Samsung Internet Android Full support 4.0 | nodejs Full support 0.12 |
Legend
- Full support
- Full support
- No support
- No support