Question

Since web workers negate the disadvantages of paused execution in JavaScript, as they will not block UI, is there a reliable method to get them to Sleep?

Either for a designated time, or until they receive a message?

Answer 1

Webworkers are essentially functions that are called via onMessage, so getting them to ‘sleep’ should simply be a matter of sending a specific message to at after a certain period of time.

Unlike threads in languages like Java, WebWorkers need not operate in a continuous (and CPU eating) loop in order to retain usefulness; they can be messaged as many times as you please.

In this example, the worker ‘sleeps’ as it waits for user input.

index.html:

<script>
    var worker = new Worker("worker.js");

    worker.onmessage = function(e) {
        console.log("Send and recieved " + e.data);
    }

    function tellWorker(element) {
        var data = element.value;
        worker.postMessage(data);
    }

</script>

worker.js:

self.onmessage = function(e) {
    self.postMessage(e.data);
}

Forgive me if I misread your question.

Edit:
Another possibility is, assuming the WebWorker is running in a setTimeout loop, listen for a message that could call clearTimeout while a user is doing something.

---

Update:

This code will create an object, modify it via the worker, and then modify it again after the parent page adjusts a flag:

index.html:

<input type="button" value="start" onclick="startWork()" /><br>
<input type="button" value="passObject" onclick="finishWork()" />

<script>
    var worker = new Worker("worker.js");

    var incompleteObject = {
        val     : 0,
        done    : false
    };


    worker.onmessage = function(e) {
        console.log("Exit Status: ");
        console.log(e.data);
    }

    function startWork() {
        worker.postMessage(incompleteObject);
    }
    function finishWork() {
        incompleteObject.done = true;
        worker.postMessage(incompleteObject);
    }

</script>

worker.js:

self.onmessage = function(e) {

    var obj = e.data;

    if(obj.done == false) {
        obj.val = 2;
    } else {
        obj.val = 4;
    }

    self.postMessage(obj);

}