Optimizing AngularJS promises for better performance

Question

Optimizing AngularJS promises for better performance

I have spent a considerable amount of time researching this topic, however, the tutorials and guides I've come across have varied significantly, making it difficult for me to fully understand this concept.

What I aim to accomplish is as follows:

1) Initiate a straightforward http request from our server [Using any API for illustration purposes]

2) Execute a function with data retrieved in step (1). [Removing a property from the object]

3) Utilize the result and length from step (2) to carry out a loop of $http requests to our server. [Or any server]

4) This will yield 6 distinct objects. Apply a function to these 6 objects. [Adding a property]

5) Only after completing all the aforementioned steps, execute a separate function [Logging "finished"]

How can promises be used to achieve this? How do I pass data from step (1) through a promise to step (2)? Is this the correct approach to accomplish my task?

If someone could demonstrate how this structure should be organized, it would be extremely beneficial; I have kept the functions simple for the sake of clarity in this inquiry.

javascript angularjs

Answer 1

Answer №1

Indeed, utilizing promises is a great way to organize solutions for these types of issues.

Below is a simplified solution, presented in pseudo-code form:

$http(...)
    .then(function(response) {
        // handle response data, such as:
        var list = reponse.data.list;
        // return the data for use in the next 'then'.
        return list;
    })
    .then(function(list) {
        var promises = [];
        angular.forEach(list, function(item) {
            // make a request for each item
            var promise = $http(...).then(function(itemResponse) {
                itemResponse.extraProperty = true;
                return itemResponse;
            });
            // create an array of promises
            promises.push(promise);
        });
        // merge all promises and return for the next then()
        return $q.all(promises);
    })
    .then(function(itemsList) {
        // itemsList now contains an array of processed item responses.
        console.log(itemsList);
    });

(Please note that this code has not been tested.)

The example demonstrates how you can pass values in callbacks to be used in the subsequent then() or pass a promise to trigger the next callback upon resolution. Using $q.all() combines multiple promises into one, resolving only when all have resolved.

Edit: It is possible to omit these three lines:

        return list;
    })
    .then(function(list) {

However, including them enhances readability by clearly separating tasks.

Answer 2

Indeed, utilizing promises is a great way to organize solutions for these types of issues.

Below is a simplified solution, presented in pseudo-code form:

$http(...)
    .then(function(response) {
        // handle response data, such as:
        var list = reponse.data.list;
        // return the data for use in the next 'then'.
        return list;
    })
    .then(function(list) {
        var promises = [];
        angular.forEach(list, function(item) {
            // make a request for each item
            var promise = $http(...).then(function(itemResponse) {
                itemResponse.extraProperty = true;
                return itemResponse;
            });
            // create an array of promises
            promises.push(promise);
        });
        // merge all promises and return for the next then()
        return $q.all(promises);
    })
    .then(function(itemsList) {
        // itemsList now contains an array of processed item responses.
        console.log(itemsList);
    });

(Please note that this code has not been tested.)

The example demonstrates how you can pass values in callbacks to be used in the subsequent then() or pass a promise to trigger the next callback upon resolution. Using $q.all() combines multiple promises into one, resolving only when all have resolved.

Edit: It is possible to omit these three lines:

        return list;
    })
    .then(function(list) {

However, including them enhances readability by clearly separating tasks.

Answer 3

Answer №2

Review the code snippet below for potential syntax errors, but focus on the overall structure. In Step3, there are six $http requests that need to be completed before a unique response object (an array) is returned, each containing the response for every $http request.

//Step 1
var Step1 = function () {
    $http.get('api/controller').success(function (resp) {
        var object1 = resp;
        Step2(object1);
        Step3(object1).then(function (resp) {
            //resp.data is an array with responses from each $http request
            Step4(resp);
            Step5();
        });
    });
}

//Step2
var Step2 = function(obj){
    //perform actions on the object
}
//Step3
var Step3 = function (object1) {
            var call = $q.defer();
            var get1 = $http.get(object1[0].url);
            var get2 = $http.get(object[1].url2);
            //...
            var get6 = $http.get(object[5].url6);

            $q.all([get1, get2,..get6]).then(function (resp) {
                call.resolve(resp);
            });
            return call.promise;
        }
//Step4
var Step4 = function (resp) {
    for (var i=0; i<resp.data.lenght;i++){
        PerformAction(resp.data[i]);
    };
}
//Step5
var Step5 = function () {
    alert("Process Complete");

}

Step1(); //Invoke Step1 function

Answer 4

Review the code snippet below for potential syntax errors, but focus on the overall structure. In Step3, there are six $http requests that need to be completed before a unique response object (an array) is returned, each containing the response for every $http request.

//Step 1
var Step1 = function () {
    $http.get('api/controller').success(function (resp) {
        var object1 = resp;
        Step2(object1);
        Step3(object1).then(function (resp) {
            //resp.data is an array with responses from each $http request
            Step4(resp);
            Step5();
        });
    });
}

//Step2
var Step2 = function(obj){
    //perform actions on the object
}
//Step3
var Step3 = function (object1) {
            var call = $q.defer();
            var get1 = $http.get(object1[0].url);
            var get2 = $http.get(object[1].url2);
            //...
            var get6 = $http.get(object[5].url6);

            $q.all([get1, get2,..get6]).then(function (resp) {
                call.resolve(resp);
            });
            return call.promise;
        }
//Step4
var Step4 = function (resp) {
    for (var i=0; i<resp.data.lenght;i++){
        PerformAction(resp.data[i]);
    };
}
//Step5
var Step5 = function () {
    alert("Process Complete");

}

Step1(); //Invoke Step1 function

Answer 5

Answer №3

Having trouble with the implementation? Consider incorporating $q.all():

var config1={method:'GET',url:'/api/...'};

$http(config1).success(function(resultsFrom1){
  functionForResultsOf1(resultsFrom1);
})


var functionForResultsOf1 = function(resultsOf1){
//modify results synchronously
resultsOf1.splice()...;
var promises=makePromises(*pass whatever you want*);
 $q.all(promises).then(function(aggregateOfAllCallsToServer){
    angular.forEach(aggregateOfAllCallsToServer,function(data){
     //manipulate data from server calls

    })

    console.log("finished");

 })
}

 var makePromises = function(serverUrls){

          var promises = [];
          angular.forEach(serverUrls, function(url) {

          var promise=$http({
                url   : '/api/'+url,
                method: 'GET',
          })

          promises.push(promise);
    });

    return $q.all(promises);
 }

Answer 6

Having trouble with the implementation? Consider incorporating $q.all():

var config1={method:'GET',url:'/api/...'};

$http(config1).success(function(resultsFrom1){
  functionForResultsOf1(resultsFrom1);
})


var functionForResultsOf1 = function(resultsOf1){
//modify results synchronously
resultsOf1.splice()...;
var promises=makePromises(*pass whatever you want*);
 $q.all(promises).then(function(aggregateOfAllCallsToServer){
    angular.forEach(aggregateOfAllCallsToServer,function(data){
     //manipulate data from server calls

    })

    console.log("finished");

 })
}

 var makePromises = function(serverUrls){

          var promises = [];
          angular.forEach(serverUrls, function(url) {

          var promise=$http({
                url   : '/api/'+url,
                method: 'GET',
          })

          promises.push(promise);
    });

    return $q.all(promises);
 }

Optimizing AngularJS promises for better performance

Answer №1

Answer №2

Answer №3

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