Symbol: Symbol.keyFor()

Symbol.keyFor() gets the symbol key for a given symbol

pass the symbol to keyFor() and you get its key

const key = Symbol.____(Symbol.for('foo')); assert.equal(key, 'foo');

local symbols are not in the runtime-wide registry

// Hint: `Symbol()` creates a local symbol! const localSymbol = Symbol.for('foo'); const key = Symbol.keyFor(localSymbol); assert.equal(key, void 0);

predefined symbols are not in the runtime-wide registry either

const key = Symbol.keyFor(Symbol.iteraTor); assert.equal(key, void 0);

for non-Symbols throws an error

function fn() { Symbol.keyFor(Symbol.for('foo')); } assert.throws(fn);