Can I Use $q.all In AngularJS With A Function That Does Not Return A .promise?
If I have the following functions: doTask1: function ($scope) { var defer = $q.defer(); $http.get('/abc') .success(function (data) { defe
Solution 1:
$q.when is used in scenarios where you don't know upfront whether the function is returning a promise or a direct value.
The following example/plunker shows a method, whose result is used in $q.all, and which returns different type of object (int or promise) every time it's called:
app.controller('MainController', function($scope, $q, $http) {
var count = 0;
function doTask1() {
var defer = $q.defer();
$http.get('abc.json')
.success(function (data) {
defer.resolve(data);
})
.error(function () {
defer.reject();
});
return defer.promise;
}
/**
* This method will return different type of object
* every time it's called. Just an example of an unknown method result.
**/
function doTask2() {
count++;
var x = 99;
if(count % 2){
console.log('Returning', x);
return x;
} else {
var defer = $q.defer();
defer.resolve(x);
console.log('Returning', defer.promise);
return defer.promise;
}
}
$scope.fetchData = function(){
// At this point we don't know if doTask2 is returning 99 or promise.
// Hence we wrap it in $q.when because $q.all expects
// all array members to be promises
$q.all([
$q.when(doTask1()),
$q.when(doTask2())
])
.then(function(results){
$scope.results = results;
});
};
});
<body ng-app="myApp" ng-controller='MainController'>
<button ng-click="fetchData()">Run</button>
<pre>{{results|json}}</pre>
</body>
Solution 2:
is there an easier way to do this [than manually constructing and resolving a deferred and returning a promise]?
Yes, use the $q.when function:
doTask2: function ($scope) {
return $q.when( 99 );
},
However, you don't actually need to do this. $q.all will - though not stated in the docs - also work with non-promise values (implementation calls _ref which converts it). So just
return 99;
is fine as well. However, if you know beforehand that it's synchronous, using promises doesn't seem to make much sense.
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