gistfile1.js

var BuyThisWorld = function BuyThisWorld(callback) {
  this.browser = document.querySelector('iframe');
	callback();
};

// DSL

BuyThisWorld.prototype.test = function(callback) {
	if (this.browser.contentDocument.querySelector('p').innerText === "Yup") {
		callback;
	}
	else {
		callback.fail();
	}
};

// helpers

BuyThisWorld.prototype.visit = function(url, callback) {
	this.browser.addEventListener('load', callback);
	// src after to avoid instant load problem
	this.browser.src = url;
};