The Symbol.keyFor() static method retrieves a shared symbol
key from the global symbol registry for the given symbol.
Syntax
Symbol.keyFor(sym)
Parameters
sym- : Symbol, required. The symbol to find a key for.
Return value
A string representing the key for the given symbol if one is found on the global registry; otherwise, undefined.
Examples
Using keyFor()
const globalSym = Symbol.for("foo"); // create a new global symbol
Symbol.keyFor(globalSym); // "foo"
const localSym = Symbol();
Symbol.keyFor(localSym); // undefined
// well-known symbols are not symbols registered
// in the global symbol registry
Symbol.keyFor(Symbol.iterator); // undefined