A naive and simple experiment at setImmediate/clearImmediate polyfilling

setimmedate.js

(function (global, rand) {
    var prefix = "setImmediate-";
    var counter = 0;
    var tasks = {};

    global.setImmediate = function (cb, params) {
        var id = prefix + counter++ + rand();
        tasks[id] = {
            fn: cb, p: params || []
        };
        window.postMessage(id, "*");
    };

    global.clearImmediate = function (cb) {
        Object.keys(tasks).some(function (key) {
            var task = tasks[key];

            if (task && task.fn === cb) {
                delete tasks[key];
                return true;
            }

            return false;
        });
    };

    runTask = function (e) {
        var task;

        if (! e.data.substr(0, prefix.length) === prefix) {
            return;
        }

        task = tasks[e.data];

        if (! task || typeof task.fn !== "function") {
            return;
        }

        task.fn.apply(global, task.p);
        
        delete tasks[key];
    };

    global.addEventListener("message", runTask, false);
}(window, Math.random));

On MS's demo for the setImmediate API copy and paste the following snippet to your console, then run the setImmediate version of quicksort

(function (g,s,d) {
    with (s) {
        src="https://gist.github.com/nikcorg/5959044/raw/82dad99f36f7787d26c69a7eb0179a19ab4fe11d/setimmedate.js";
        type="text/javascript";
        onload=function(){g.msSetImmediate=g.setImmediate;};
    }
    d.appendChild(s);
    g.browserSupportsSetImmediate=true;
}(window,document.createElement("script"),document.body));