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.

key

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

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

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.

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

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');

• Symbol.keyFor()