Angular q.all: comparing immediate and delayed responses

Question

Angular q.all: comparing immediate and delayed responses

Seeking advice on methodology: I currently utilize $q.all to handle multiple promises in a single return, processing all results as one request.

For instance:

$q.all([promise1(),promise2(),promise3(),promise(4),promise5()])..then(function(response){ ...}

However, I have observed that different promises are often returned at varying time frames. These promises are all http calls to third party sites. When one promise is delayed by 8 or 14 seconds, the final results of all promises are similarly delayed. A case of the 'slowest link' syndrome.

Is there an alternative method to simultaneously call all promises while allowing results to be processed and displayed to the user as they arrive, rather than waiting for all promises to return before processing them collectively?

javascript angularjs real-time angular-promise q

Answer 1

Answer №1

If you prefer to use them separately as suggested in the feedback, that is an option. However, for those who are interested in calling all of them simultaneously and handling them within one promise, the notify-callback of the promise can be utilized. I've developed an extension for $q that leverages the notify() function to resolve the promises collectively:

app.run(function($q){
    $q.each = function(promises){
        var deferred = $q.defer();

        promises.forEach(function(promise){
            promise.then(function(data){
                deferred.notify(data);
            });
        });
        return deferred.promise;
    };
});

Although this implementation is simplistic and lacks error handling, it provides a basic understanding of the process involved.

To use this extension, simply follow this structure:

var promises = [promise1(), promise2(), promise3(), promise(4), promise5()];

$q.each(promises).then(null, null, function(data){
    console.log(data);  // This function is executed upon resolution of each promise.
});

For a demonstration of this concept in action, you can view the following Plunker

Answer 2

If you prefer to use them separately as suggested in the feedback, that is an option. However, for those who are interested in calling all of them simultaneously and handling them within one promise, the notify-callback of the promise can be utilized. I've developed an extension for $q that leverages the notify() function to resolve the promises collectively:

app.run(function($q){
    $q.each = function(promises){
        var deferred = $q.defer();

        promises.forEach(function(promise){
            promise.then(function(data){
                deferred.notify(data);
            });
        });
        return deferred.promise;
    };
});

Although this implementation is simplistic and lacks error handling, it provides a basic understanding of the process involved.

To use this extension, simply follow this structure:

var promises = [promise1(), promise2(), promise3(), promise(4), promise5()];

$q.each(promises).then(null, null, function(data){
    console.log(data);  // This function is executed upon resolution of each promise.
});

For a demonstration of this concept in action, you can view the following Plunker

Answer 3

Answer №2

It is important to remember that functions like then() or $q.all() do not control the order in which promises are executed; they simply define when you want a response. Even though myPromise.then(doSomething) may suggest otherwise, the promises begin running as soon as they are created.

Additionally, $q.all does not combine promises in the traditional sense; instead, it creates a new promise that resolves or rejects based on the outcomes of the original promises. This means a promise is not restricted to a single handler...

promise1.then(function () {
    //logic that only depends on promise1 and does not require the others
});
$q.all(promise1, promise2, ...).then(function () {
    //logic that can only be executed once all promises are completed
});

Answer 4

It is important to remember that functions like then() or $q.all() do not control the order in which promises are executed; they simply define when you want a response. Even though myPromise.then(doSomething) may suggest otherwise, the promises begin running as soon as they are created.

Additionally, $q.all does not combine promises in the traditional sense; instead, it creates a new promise that resolves or rejects based on the outcomes of the original promises. This means a promise is not restricted to a single handler...

promise1.then(function () {
    //logic that only depends on promise1 and does not require the others
});
$q.all(promise1, promise2, ...).then(function () {
    //logic that can only be executed once all promises are completed
});

Angular q.all: comparing immediate and delayed responses

Answer №1

Answer №2

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