in JavaScript, how to wrap a promise in timeout?

Question

It's a common pattern to implement timeout of some asynchronous function, using deffered/promise:

// Create a Deferred and return its Promise
function timeout(funct, args, time) {
    var dfd = new jQuery.Deferred();

    // execute asynchronous code
    funct.apply(null, args);

    // When the asynchronous code is completed, resolve the Deferred:
    dfd.resolve('success');

    setTimeout(function() {
        dfd.reject('sorry');
    }, time);
    return dfd.promise();
}

Now we can execute some asynchronous function called myFunc and handle timeout:

// Attach a done and fail handler for the asyncEvent
$.when( timeout(myFunc, [some_args], 1000) ).then(
    function(status) {
        alert( status + ', things are going well' );
    },
    function(status) {
        alert( status + ', you fail this time' );
    }
);

OK, let's make a twist in this story! Imagine that the myFunc itself returns a promise (NOTE: promise NOT deferred and I can't change it):

function myFunc(){
    var dfd = new jQuery.Deffered();
    superImportantLibrary.doSomething(function(data)){
       if(data.length < 5){
            dfd.reject('too few data');
       }
       else{
           dfd.resolve('success!');
       }
    }, {'error_callback': function(){
        dfd.reject("there was something wrong but it wasn't timeout");}
    }});
    return dfd.promise();
}

Now if I wrap myFunc in timeout, I will loose the ability to handle errors different then timeout. If myFunc emit progress events, I will loose this as well.

So the question is: how to modify timeout function so it can accept functions returning promises without loosing their errors/progress information?

Answer 1

function timeout(funct, args, time) {
    var deferred = new jQuery.Deferred(),
        promise = funct.apply(null, args);

    if (promise) {
        $.when(promise)
            .done(deferred.resolve)
            .fail(deferred.reject)
            .progress(deferred.notify);
    }

    setTimeout(function() {
        deferred.reject();
    }, time);

    return deferred.promise();
}