How can I ensure that my function only returns a value once the ajax call has finished?

Question

How can I ensure that my function only returns a value once the ajax call has finished?

Using mootools, I have a function that triggers an ajax script to retrieve a value. However, the function seems to return before the AJAX call is completed!

What could be causing this issue...

function getCredits() {
    var loadGlobalTab = new Request.JSON({
        url: {my api, url removed for security},
        evalScripts : true,
        async: false,    // Tried to prevent the function from returning too soon, but no luck.
        onSuccess: function(returnInfo) {
            alert(returnInfo.data.total);
            return returnInfo.data.total;
        }
    }).send(sendData);    // sendData variable defined earlier
}

The alert displays the correct value, indicating the AJAX call works. However, the function itself does not return anything, suggesting it ends prematurely while the AJAX call is still in progress.

As an experiment, I added return 100 at the end, and the function indeed returned 100.

javascript ajax mootools

Answer 1

Answer №1

update oh no, got interrupted by a phone call. oh well!

Ajax functions asynchronously and using async: false is not the recommended approach. Instead, create a second callback function to handle the query result directly from onComplete/onSuccess.

If blocking is absolutely necessary, then this method will work effectively:

var blockingCheck = function() {
    var obj = {};
    new Request.JSON({
        url: '/echo/json/',
        data: {
            json: JSON.encode({
                text: 'some text',
                array: [1, 2, 'three'],
                object: {
                    par1: 'another text',
                    par2: [3, 2, 'one'],
                    par3: {}
                }
            }),
            delay: 3
        },
        async: false,
        onSuccess: function(response) {
            obj = response;
        }
    }).send();

    return obj;
};

console.log(blockingCheck());

http://jsfiddle.net/dimitar/eG4t2/

Answer 2

update oh no, got interrupted by a phone call. oh well!

Ajax functions asynchronously and using async: false is not the recommended approach. Instead, create a second callback function to handle the query result directly from onComplete/onSuccess.

If blocking is absolutely necessary, then this method will work effectively:

var blockingCheck = function() {
    var obj = {};
    new Request.JSON({
        url: '/echo/json/',
        data: {
            json: JSON.encode({
                text: 'some text',
                array: [1, 2, 'three'],
                object: {
                    par1: 'another text',
                    par2: [3, 2, 'one'],
                    par3: {}
                }
            }),
            delay: 3
        },
        async: false,
        onSuccess: function(response) {
            obj = response;
        }
    }).send();

    return obj;
};

console.log(blockingCheck());

http://jsfiddle.net/dimitar/eG4t2/

Answer 3

Answer №2

When working with ajax, it is important to remember that it is asynchronous.

This means that JavaScript will continue execution without waiting for the response, so if there is no immediate return, nothing will be returned.

A recommended practice is to use a callback function instead of relying on a return statement:

function getCredits() {
    var loadGlobalTab = new Request.JSON({
        url: {my api, url removed for security},
        evalScripts : true,
        headers: {'ACCEPT': 'json','X_REQUESTED_WITH':'jsonhttprequest'},
        onSuccess: function(returnInfo) {
            alert(returnInfo.data.total);
            //go to callback
            getCredits_Callback(returnInfo.data.total);
        }
    }).send(sendData);    // Where sendData has been defined prior
}

function getCredits_Callback(total){
   //perform actions using total
}

Another way to handle this is:

function getCredits() {
    var loadGlobalTab = new Request.JSON({
        url: {my api, url removed for security},
        evalScripts : true,
        headers: {'ACCEPT': 'json','X_REQUESTED_WITH':'jsonhttprequest'},
        onSuccess: getCredits_Callback
    }).send(sendData);    // Where sendData has been defined prior
}

function getCredits_Callback(returnInfo){
   //do something with returnInfo
}

Answer 4

When working with ajax, it is important to remember that it is asynchronous.

This means that JavaScript will continue execution without waiting for the response, so if there is no immediate return, nothing will be returned.

A recommended practice is to use a callback function instead of relying on a return statement:

function getCredits() {
    var loadGlobalTab = new Request.JSON({
        url: {my api, url removed for security},
        evalScripts : true,
        headers: {'ACCEPT': 'json','X_REQUESTED_WITH':'jsonhttprequest'},
        onSuccess: function(returnInfo) {
            alert(returnInfo.data.total);
            //go to callback
            getCredits_Callback(returnInfo.data.total);
        }
    }).send(sendData);    // Where sendData has been defined prior
}

function getCredits_Callback(total){
   //perform actions using total
}

Another way to handle this is:

function getCredits() {
    var loadGlobalTab = new Request.JSON({
        url: {my api, url removed for security},
        evalScripts : true,
        headers: {'ACCEPT': 'json','X_REQUESTED_WITH':'jsonhttprequest'},
        onSuccess: getCredits_Callback
    }).send(sendData);    // Where sendData has been defined prior
}

function getCredits_Callback(returnInfo){
   //do something with returnInfo
}

Answer 5

Answer №3

The function isn't outputting anything because the return statement is targeting an object attribute instead of the intended variable. It might be beneficial to delegate the "onSuccess" function to a separate handler function, allowing you to manage the return values outside of a closure.

Answer 6

The function isn't outputting anything because the return statement is targeting an object attribute instead of the intended variable. It might be beneficial to delegate the "onSuccess" function to a separate handler function, allowing you to manage the return values outside of a closure.

How can I ensure that my function only returns a value once the ajax call has finished?

Answer №1

Answer №2

Answer №3

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