AngularJS promises, how to $q.first.then(others[])

Question

In an AngularJs controller I need to ensure a paramount variable initialized before performing other tasks.

var firstPromise = $scope.watch("myParamount"...); // from ng-init
var otherPromises = []; // once obtained myParamount, do others

// something like this?!
$q.firstPromise.then.all(otherPromises).then(function(){
    console.log("first, then otherPromises completed!");
})

How to fix this "fake" code?

This is unrelated to the question but what is `$scope.watch`? Did you perhaps mean `$scope.$watch`? In that case, it does't return a promise, but a deregistration listener. — Nikolaj Dam Larsen, Jul 28 '17 at 10:53
@NikolajDamLarsen so, this is the cause you downvoted the OP? I didn't know that — serge, Jul 28 '17 at 11:00

score 1 · Answer 1 · answered Jul 28 '17 at 11:31

1

Assuming those are actual promises, you should be able to use promise chaining to do something like this.

Here's a sample using timeouts for illustrative purposes:

var firstPromise = $timeout(echo('first'), 1000);

firstPromise.then(function(data){
    console.log(data); // 'first'
    return $q.all([  // Other promises
        $timeout(echo('other 1'), 1000),
        $timeout(echo('other 2'), 500),
        $timeout(echo('other 3'), 1500)
    ]);;
}).then(function(data){
    console.log(data); // ['other 1', 'other 2', 'other 3']
});

function echo(v) { return function(){ return v; } }

That is one way to chain them, so the other promises isn't run until the first has resolved.

answered Jul 28 '17 at 11:31

Nikolaj Dam Larsen

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what are that magic 1000, 500, 1500? what if the first taks take more than 1000ms? – serge Jul 28 '17 at 12:24
Those are just random values to illustrate that the promises might finish at different times. The calls to $timeout is just placeholders for real promises. So for instance in a real scenario it might look like this: `var firstPromise = $http.get('/someurl');` – Nikolaj Dam Larsen Jul 28 '17 at 12:45
I understand now better. Just question about `$watch`, is it possible to wait for the first initialization of `myParamount` (maybe also `myParamount2`), then query all other promises? – serge Jul 28 '17 at 12:55
You ought to create that as a separate SO question. I have an idea how to answer it, but it wouldn't really be fitting to include it in the answer above. There's two parts to it. 1) Only firing a $watch once. 2) awaiting a $watch using a promise. – Nikolaj Dam Larsen Jul 28 '17 at 13:07

AngularJS promises, how to $q.first.then(others[])

1 Answers1