deferring $.ajax requests

Question

I have to make N ajax requests. Each $.ajax call returns a Deferred, but also immediately performs the ajax request. What i want to do is get the Deferreds for all N requests, but only have them performed gradually (say through a setInterval loop). Is it possible to do this?

Answer 1

The browser will by itself limit the number of parallel ajax requests made to a single server (e.g. 4 or 8 at the same time).

If the limit it's not enough, you could make a queue and schedule some queries:

var queue = [];
queue.push(function() { 
    return $.ajax(...);
});
queue.push(function() { 
    return $.ajax(...);
});
...

Then run e.g. 2 of the queries, and each time one finishes, take an other from the queue and run it:

function runNext() {
    var fun = queue.shift();
    if (fun) {
        fun().always(runNext);
    }
}
for (var i = 0; i < 2; ++i) {
    runNext();
}