Angular fire 2异步调用一次，但在第一次完成之前不处理第二次回调

Question

I'm using Angular's $q service to make async requests. I have 2 requests like so (assume I have an angular service named MyService that handles these requests):

MyService.Call1().then(function() {
    //do all the first callback's processing here without waiting for call 2
});

MyService.Call2().then(function() {
    //wait for results of first callback before executing this
});

I have no guarantee that the second call will finish after the first, but I need the results of call 1 in order to do processing in call 2. I understand that I could chain the promises together, meaning that call 2 waits for call 1 to finish before the request is made, but I want to fire both requests at the same time since I have all the data required to do so. What's the best way to do that?

Edit: I can use the results of the first call immediately. They drive some charts on my page. I don't want the first call to wait on the second call to do its processing. I think that rules out mechanisms like $q.all()

Answer 1

You can do both calls in parallel with all

$q.all([MyService.Call1(), MyService.Call2()]).then(function() {
  // ...code dependent on both calls resolving.
});

Edit : In response to a comment, there are two things that might interest you. If you pass an array to all , you will find an array of resolutions as the first argument of your function inside of then . If, instead, you pass an object to all , you will find an object as your first argument with keys matching the same keys you passed into all .

$q.all([MyService.Call1(), MyService.Call2()]).then(function(arr) {
  // ...code dependent on the completion of both calls.  The result
  // of Call1 will be in arr[0], and the result of Call2 will be in
  // arr[1]
});

...and with objects

$q.all({a: MyService.Call1(), b: MyService.Call2()}).then(function(obj) {
  // ...code dependent on the completion of both calls.  The result
  // of Call1 will be in abj.a, and the result of Call2 will be in
  // obj.b
});

Answer 2

An alternative to using $q.all would be to use the first promise in the handler for the second. For example

var p1 = MyService.Call1().then(function(data) {
    return processedData;
});

MyService.Call2().then(function(call2Data) {
    return p1.then(function(call1Data) {
        // now you have both sets of data
    });
});

---

To address some comments, here's how you could handle errors / promise rejections without having to wait for both promises to resolve or creating multiple catch handlers...

var p2 = MyService.Call2().then(function(call2Data) {
    return p1.then(function(call1Data) {
        // now you have both sets of data
    });
});

// use `$q.all` only to handle errors
$q.all([p1, p2]).catch(function(rejection) {
    // handle the error here
});