is-implemented.js #1

'use strict';

var validTypes = { object: true, symbol: true };

module.exports = function () {
	var symbol;
	if (typeof Symbol !== 'function') return false;
	symbol = Symbol('test symbol');
	try { String(symbol); } catch (e) { return false; }

	// Return 'true' also for polyfills
	if (!validTypes[typeof Symbol.iterator]) return false;
	if (!validTypes[typeof Symbol.toPrimitive]) return false;
	if (!validTypes[typeof Symbol.toStringTag]) return false;

	return true;
};