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:
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 Language Specification # sec-symbol.for |
Browser compatibility
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