The Symbol.for() static 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.
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
const 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");