Javascript - synchronizing after asynchronous calls

Question

I have a Javascript object that requires 2 calls out to an external server to build its contents and do anything meaningful. The object is built such that instantiating an inst

Answer 1

Another way would be to have a sync point thanks to a timer. It is not beautiful, but it has the advantage of not having to add the call to the next function inside the callback.

Here the function execute_jobs is the entry point. it take a list of data to execute simultaneously. It first sets the number of jobs to wait to the size of the list. Then it set a timer to test for the end condition (the number falling down to 0). And finally it sends a job for each data. Each job decrease the number of awaited jobs by one.

It would look like something like that:

var g_numJobs = 0;

function async_task(data) {
    //
    // ... execute the task on the data ...
    //

    // Decrease the number of jobs left to execute.
    --g_numJobs;
}

function execute_jobs(list) {
    // Set the number of jobs we want to wait for.
    g_numJobs = list.length;

    // Set the timer (test every 50ms).
    var timer = setInterval(function() {
        if(g_numJobs == 0) {
            clearInterval(timer);
            do_next_action();
        }
    }, 50);

    // Send the jobs.
    for(var i = 0; i < list.length; ++i) {
        async_task(list[i]));
    }
}

To improve this code you can do a Job and JobList classes. The Job would execute a callback and decrease the number of pending jobs, while the JobList would aggregate the timer and call the callback to the next action once the jobs are finished.