The accepted answer is correct. I would like to provide an example to elaborate it a bit to those who aren't familiar with promise
.
Example:
In my example, I need to replace the src
attributes of img
tags with different mirror urls if available before rendering the content.
var img_tags = content.querySelectorAll('img');
function checkMirrorAvailability(url) {
// blah blah
return promise;
}
function changeSrc(success, y, response) {
if (success === true) {
img_tags[y].setAttribute('src', response.mirror_url);
}
else {
console.log('No mirrors for: ' + img_tags[y].getAttribute('src'));
}
}
var promise_array = [];
for (var y = 0; y < img_tags.length; y++) {
var img_src = img_tags[y].getAttribute('src');
promise_array.push(
checkMirrorAvailability(img_src)
.then(
// a callback function only accept ONE argument.
// Here, we use `.bind` to pass additional arguments to the
// callback function (changeSrc).
// successCallback
changeSrc.bind(null, true, y),
// errorCallback
changeSrc.bind(null, false, y)
)
);
}
$q.all(promise_array)
.then(
function() {
console.log('all promises have returned with either success or failure!');
render(content);
}
// We don't need an errorCallback function here, because above we handled
// all errors.
);
Explanation:
From AngularJS docs:
The then
method:
then(successCallback, errorCallback, notifyCallback) – regardless of when the promise was or will be resolved or rejected, then calls
one of the success or error callbacks asynchronously as soon as the
result is available. The callbacks are called with a single
argument: the result or rejection reason.
$q.all(promises)
Combines multiple promises into a single promise that is resolved when
all of the input promises are resolved.
The promises
param can be an array of promises.
About bind()
, More info here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/bind