is-implemented.js

'use strict';

module.exports = function () {
	var weakMap, x;
	if (typeof WeakMap !== 'function') return false;
	try {
		// WebKit doesn't support arguments and crashes
		weakMap = new WeakMap([[x = {}, 'one'], [{}, 'two'], [{}, 'three']]);
	} catch (e) {
		return false;
	}
	if (String(weakMap) !== '[object WeakMap]') return false;
	if (typeof weakMap.set !== 'function') return false;
	if (weakMap.set({}, 1) !== weakMap) return false;
	if (typeof weakMap.delete !== 'function') return false;
	if (typeof weakMap.has !== 'function') return false;
	if (weakMap.get(x) !== 'one') return false;

	return true;
};