AngularJS Accelerated Promises
I am having trouble getting the repeat function to work and was hoping for some help. I have a $ resource that I want to call until a success condition occurs or the maximum retries are exceeded.
The problem I seem to be running into is that in my retry function I call another promise and the condition will be checked there. I could get the code to function as expected by removing the added promise and creating a default success condition after a few tries, but I can't figure out how to properly add a new call to the function.
resource
is the fallback for the Angular $ resource that $ prom returns
My code looks like this:
resource.$promise.then(function (response) {
return keepTrying(state, 5);
}).then(function (response) {
}).catch(function (err) {
console.log(err);
});
And the keepTrying function:
function keepTrying(state, maxRetries, deferred) {
deferred = deferred || $q.defer();
resource.$promise.then(function (response) {
success = response;
});
if (success) {
return deferred.resolve(success);
} else if (maxRetries > 0) {
setTimeout(function () {
keepTrying(state, maxRetries - 1, deferred);
}, 1000);
} else if (maxRetries === 0) {
deferred.reject('Maximum retries exceeded');
}
return deferred.promise;
}
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The problem with your attempt is that you are not re-requesting the resource, but using the promise for the already requested resource over and over again.
What you need to do is use a function that (a) initiates a request and (b) returns a promise for that initiated request. Something like that:
function () { return $resource.get().$promise; }
Then you can pipe it to something like that, which will do the repetitions.
function retryAction(action, numTries) {
return $q.when().then(action)
.catch(function (error) {
if (numTries <= 0) {
throw error;
}
return retryAction(action, numTries - 1);
});
}
Here's how you do it:
retryAction(function () { return $resource.get().$promise; }, 5)
.then(function (result) {
// do something with result
});
One of the nice things about this approach is that even if the function you pass to it throws an error when called, or doesn't return a promise at all, the repeat function and return the result via resolved promises will work.
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You can implement a retryOperation function that returns a new promise on error up to the maximum number of retries passed as an argument:
function retryOperation(retryCount) {
var count = 0;
function success(result) {
return result;
}
function error(result) {
++count;
if (count <= retryCount)
return $resource(...).query().$promise.then(success, error);
throw 'max retries reached';
}
return $resource(...).query().$promise.then(success, error);
}
Using
retryOperation(3).then(
function success(result) {
// done!
},
function error(reason) {
alert(reason);
});
var app = angular.module('app', []);
app.controller('ctrl', function($q) {
function retryOperation(count) {
var retryCount = 0;
function operation() {
var deferred = $q.defer();
deferred.reject('failed');
return deferred.promise;
}
function success(result) {
return result;
}
function error(result) {
++retryCount;
if (retryCount <= count) {
alert('retrying ' + retryCount);
return operation().then(success, error);
}
throw 'maximum retries reached';
}
return operation().then(success, error);
}
retryOperation(3).then(
function success(result) {
alert('done');
},
function error(result) {
alert(result);
});
});
<html>
<head>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
</head>
<body ng-app="app" ng-controller="ctrl">
<input type="text" ng-model="name" />{{name}}
</body>
</html>
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