shell bypass 403
"use strict";
var global = require("ext/global-this")
, validTypes = { object: true, symbol: true };
module.exports = function () {
var Symbol = global.Symbol;
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;
};