へびにっき

var UnsafeWrapper = new (function() {
	var seqId = 0, waiting = {}, self = this, noop = function(){};
 
	function dispatch(data, id) {
	    var e = document.createEvent("MessageEvent");
	    e.initMessageEvent('GM_UnsafeWrapper_returned', true, false,
			       data, location.protocol + "//" + location.host,
			       id, window);
	    document.dispatchEvent(e);
	}
 
	function listen(func) {
	    document.addEventListener('GM_UnsafeWrapper_returned', func, false);
	}
 
	listen(function(e) {
		if(waiting[e.lastEventId]) {
		    waiting[e.lastEventId].call(self, JSON.parse(e.data));
		    delete waiting[e.lastEventId];
		}
	    });
 
	this.exec = function(func, args, callback) {
	    var userFunc = "("+ func +").apply(null,"+ JSON.stringify(args || []) +")";
	    waiting[seqId] = callback || noop;
	    location.href = "javascript:void "+
	    (function(dispatch, ret, id) { dispatch(JSON.stringify(ret), id) }) +
	    "("+ dispatch +","+ userFunc +"," + JSON.stringify(seqId) +")";
	    return seqId++;
	};
 
	this.cancel = function(id) {
	    delete waiting[id];
	};
    });

with(D()) {
    function unsafeExec(func, args) {
	var d = new Deferred();
	var id = UnsafeWrapper.exec(func, args, function(ret) {
		d.call(ret);
	    });
	d.canceller = function(){ UnsafeWrapper.cancel(id) };
	return d;
    };
}

with(D()) {
 
xhttp.get("http://example.com/")
    .next(function(res) {
            var data = res.responseText;
            //....
 
	    return unsafeExec(function(data) {
                    $.each(data, function(k,v) {
                      //...
                    });
                    //...
		    return result;
		},
		[data]);
	})
    .next(function(result) {
          //...
	});
 
}

function evalInPage(func, args) {
    var argStr = JSON.stringify(args || []);
    location.href = "javascript:void "+ func +".apply(null,"+ argStr +")";
}

// データの取得は Greasemonkey で行う
GM_xmlhttpRequest({ method:"GET",
                    url: "http://example.com/api",
                    onload: function(response) {
                      var data = response.responseText;
                      //...
                      evalInPage(render, [data]);
                    }
                  });
 
// データの表示は unsafeWindow 上で行う
// jQueryなど unsafeWindow 上のライブラリが使える
function render(data) {
  $.each(data, function(k,v){
    //...
  })
}

function getUniqId() {
    do {
        var id = "_tmp" + String(Math.random()).slice(2);
    } while(document.getElementById(id));
    return id;
}
 
function evalInPage(func, args, callback) {
    var argStr = JSON.stringify(args || []),
        userFunc = "("+ func +").apply(null,"+ argStr +")";
 
    if(!callback) {
        location.href = "javascript:void "+ userFunc;
        return;
    }
 
    var div = document.createElement('div'),
        id = getUniqId();
    div.id = id;
    div.style.display = 'none';
    document.body.appendChild(div);
    div.addEventListener('DOMNodeInserted', function(e){
            callback(JSON.parse(e.target.nodeValue));
            div.parentNode.removeChild(div);
        }, false);
 
    location.href = "javascript:void "+ (function(ret, id) {
            document.getElementById(id)
            .appendChild(document.createTextNode(JSON.stringify(ret)));
        }).toString() + ".call(null,"+ userFunc +"," + JSON.stringify(id) +")";
}

evalInPage(function(obj, num) {
        //この中のコードは unsafeWindow で実行される
        return { answer: obj.a + num };
    },
    [{a:99}, 1],
    function(ret) {
        //この中のコードは Greasemonkey で実行される
	alret(ret.answer);
    });