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Automatically redirects all www.amazon.com URLs to their smile.amazon.com equivalent.
// ==UserScript==
// @name Amazon Auto-Smile
// @namespace
// @version 0.1
// @description Automatically redirects all www.amazon.com URLs to their smile.amazon.com equivalent.
// @match http://www.amazon.com/*
// @match https://www.amazon.com/*
// @run-at document-start
// @copyright 2013
// ==/UserScript==
// Only redirect if we're the top window
//
// This prevents iframes embedded within www.amazon.com pages from
// triggering redirects themselves: we only want the outer window to do that.
// Unfortunately, it has the side-effect that if amazon.com is embedded
// in a frame on some other website, we'll skip doing the redirect even though
// we're supposed to.
if (window.self === window.top) {
var new_host = window.location.host.replace(/^www\./, 'smile.');
var new_url = window.location.protocol + '//' + new_host + window.location.pathname + window.location.search + window.location.hash;
window.location.replace(new_url);
}