如何循环遍历一组异步作业，并分别执行它们？

Question

There is an array of jobs, say 'asking user to fill a form', 'issue an ajax request', etc.

I need to run these jobs one after another and finally call a complete() method.

Something like:

var jobs = [11, 22, 33, 44, ...];

for(var i = 0; i < jobs.length; i++) {
   alert('Starting job #' + i);

   // chooseJobOperator shows a form and wait for user to <select> a member
   // and click save <button>
   async(chooseJobOperator(jobs[i]));

   alert('Job #' + i + ' is done, now for-loop will continue');
}

alert('All jobs are done now.');
complete();

When my job is for example showing a prompt() I don't need to do anything, since prompt is a synchronous method, but what about asynchronous methods?

Is it possible to do so using jQuery.Deffered ?

Answer 1

You can try this

var jobs = [11, 12, 14, 15];
function doTheJob() {
    if (jobs.length === 0) {
        alert('All jobs are done now.');
        complete();
        return;
    }

    var job_Id = jobs.pop();
    $.ajax({
        url: "/DoTheJob",
        complete: function () {
            doTheJob();
        }
    });
};

Answer 2

Maybe there is better approach, but I would use $.when function for this. Here is an example of how it could look:

var jobs = [1, 2, 3];

var d = $.Deferred(),
    stack = [];

for (var i = 0; i < jobs.length; i++) {
    stack.push(async(jobs[i]));
}

$.when.apply($, stack).done(function() {
    alert('All done');
});

function async(type) {
    alert('Starting job #' + type);
    return $.Deferred(function() {
        var self = this;
        setTimeout(function() {
            alert('Job #' + type + ' is done');
            self.resolve();
        }, 1000 * type);
    });
}

I used setTimeout as asynchronous operation.

http://jsfiddle.net/rs3Qv/1/