Perhaps my article on $q can provide some assistance to you.
Exploring the World of $q
$q serves as an angular defined service, offering similar functionalities to new Promise(). However, $q elevates the experience by providing additional features that simplify complex tasks for developers.
Below is a simple example showcasing how to create a promise using $q:
angular.module("app",[])
.controller("ctrl",function($scope,$q){
var work = "resolve";
var promise = $q(function(resolve, reject) {
if (work === "resolve") {
resolve('response 1!');
} else {
reject('Oops... something went wrong');
}
});
promise.then(function(data) {
alert(data)
})
})
The Power of $q.defer()
When utilizing $q.defer(), an instance of the promise constructor is returned. This allows access to various methods and properties associated with the object.
resolve(value) – resolves the derived promise with a specific value or rejection if constructed via $q.reject.
reject(reason) – rejects the derived promise with a specified reason, equivalent to resolving it with a rejection through $q.reject.
notify(value) - provides updates regarding the status of the promise's execution, allowing multiple calls before resolution or rejection.
promise – {Promise} – represents the promise object linked to this deferred.
Check out the example below:
angular.module("app",[])
.controller("ctrl",function($scope,$q){
var work = "resolve";
function getData(){
var obj = $q.defer();
if (work === "resolve") {
obj.resolve('response 1!');
} else {
obj.reject('Oops... something went wrong');
}
return obj.promise;
}
getData().then(function(data) {
alert(data)
})
})
Embracing $q.all()
For users needing to send multiple requests simultaneously, leveraging the $q.all() service proves beneficial.
$q.all([$http.get('data1.json'),$http.get('data2.json')])
.then(function(response){
console.log(response[0].data) // data1.json response
console.log(response[1].data) // data1.json response
})
In this scenario, two HTTP requests are sent concurrently to separate JSON files, returning responses in an array matching the order of the requests.
Understanding $q.race()
Similar to $q.all(), $q.race() focuses on returning only one response from multiple requests, specifically the first request executed. All requests are still initiated, but the method solely presents the initial response received.
$q.race([$http.get('data1.json'),$http.get('data2.json')])
.then(function(response){
console.log(response[0].data) // return one response
})
With $q.race(), either data1.Json or data2.json could be the resulting response. The uncertainty lies in the fact that only the initial executed request's response is resolved, ideal for handling bulk requests where viewing all responses is unnecessary.
In Conclusion
Employ $q for constructing promises from non-promise Objects/callbacks, while tapping into the capabilities of $q.all() and $q.race() for seamless promise management.