hasSymbols.js

'use strict';

var keys = require('object-keys');

module.exports = function hasSymbols() {
	if (typeof Symbol !== 'function' || typeof Object.getOwnPropertySymbols !== 'function') { return false; }
	if (typeof Symbol.iterator === 'symbol') { return true; }

	var obj = {};
	var sym = Symbol('test');
	var symObj = Object(sym);
	if (typeof sym === 'string') { return false; }

	if (Object.prototype.toString.call(sym) !== '[object Symbol]') { return false; }
	if (Object.prototype.toString.call(symObj) !== '[object Symbol]') { return false; }

	// temp disabled per https://github.com/ljharb/object.assign/issues/17
	// if (sym instanceof Symbol) { return false; }
	// temp disabled per https://github.com/WebReflection/get-own-property-symbols/issues/4
	// if (!(symObj instanceof Symbol)) { return false; }

	var symVal = 42;
	obj[sym] = symVal;
	for (sym in obj) { return false; }
	if (keys(obj).length !== 0) { return false; }
	if (typeof Object.keys === 'function' && Object.keys(obj).length !== 0) { return false; }

	if (typeof Object.getOwnPropertyNames === 'function' && Object.getOwnPropertyNames(obj).length !== 0) { return false; }

	var syms = Object.getOwnPropertySymbols(obj);
	if (syms.length !== 1 || syms[0] !== sym) { return false; }

	if (!Object.prototype.propertyIsEnumerable.call(obj, sym)) { return false; }

	if (typeof Object.getOwnPropertyDescriptor === 'function') {
		var descriptor = Object.getOwnPropertyDescriptor(obj, sym);
		if (descriptor.value !== symVal || descriptor.enumerable !== true) { return false; }
	}

	return true;
};