HTML 5 Web Workers

<p>计数:<output id="result"></output></p>
<button onclick="startWorker()">开始 Worker</button>
<button onclick="stopWorker()">停止 Worker</button>

    /**
     * web worker
     */
    var w;
    function startWorker(){
        if (typeof(Worker)!=="undefined"){
            if (typeof(w)=="undefined"){
                w = new Worker("/js/demo_workers.js");
            }
            w.onmessage = function (event) {
                alert(‘a‘);
                document.getElementById("result").innerHTML = event.data;
            }
        } else {
            document.getElementById("result").innerHTML = "Sorry, your browser does not support Web Workers...";
        }
        alert(‘b‘);
    }
    function stopWorker() {
        w.terminate();
    }

postMessage(1);