amazon.js

u = location.href;
t = "takuya-hateblo-22";
a = (function(url, tag) {
    asin = (function(url) {
        if (r = url.match(/gp\/product\/([^\/]+)/)) {
            return r[1];
        } else if (r = url.match(/dp\/([^\/]+)/)) {
            return r[1];
        } else {
            return;
        }
    })(url);
    if(asin){
	    return "http://amazon.jp/dp/" + asin + "/?tag=" + tag;

    }else{
		    u = new URL(url)
		    ret = u.search.replace("?","").split(/&/)
		    ret.unshift(("tag="+tag));
		    u.search = ret.join("&")
		    u.hostname = "amazon.jp"
		    return u.toString();
    }

})(u, t);
prompt("", a);