CODEWITHSUNDEEP
jqueryjsonalertassign
vinay kumar
vinay kumar

Reputation: 1449

JavaScript: unable to assign value without alert

I have declared this function in .js file and calling it in .html file.

function getTotalPages() {
    var valuePage;
    $.getJSON('Data/product.json').
        done(function(data) {
        $.each(data, function(key, value) {
                valuePage=value;
            });
        });
    //alert('out');
    return valuePage;
}

The above function returns the "undefined" without "alert", with alert it is working good. Can any one help me on this.

Thank you In advance.

Upvotes: 0

Views: 297

Answers (3)

Minko Gechev
Minko Gechev

Reputation: 25682

It's not working because your ajax request is asynchronous. With alert you have a timeout after which the value is returned. You can make your script work by adding async: false (note for cross-domain requests using jsonp you cannot make synchronous request!) but actually I don't recommend you because your JS will block until the request is ready. Better approach is to use a callback:

function getTotalPages(callback) {
  var valuePage;
    $.getJSON('Data/product.json').
        done(function(data) {
            $.each(data, function(key, value) {
            if (typeof callback === 'function') {
                callback(value);
            }
        });
    });
}

Here is an example how you can do this using asynchronous request:

function getResult(callback) {
    var url = 'https://api.twitter.com/1/statuses/user_timeline.json?include_entities=true&include_rts=true&screen_name=mgechev&count=3';
    $.ajax({
        url: url,
        success: function (data) {
            if (typeof callback === 'function') {
                callback(data);
            }
        },
        dataType: 'jsonp'
    });
}

getResult(function (data) {
    var variable = data;
    alert(variable);
});​

JSFiddle: http://jsfiddle.net/vWnHJ/

In the example I pass function to the getResult function and call the given function with the data received from the request.

Upvotes: 2

elclanrs
elclanrs

Reputation: 94121

AJAX is asynchronous, by the time you close the alert message the returned value will be resolved, but without the alert it would be too early. You can either make a synchronous request or use a callback.

Upvotes: 1

devnull69
devnull69

Reputation: 16564

This issue has been answered a thousand times. It's about 'there is no way to return any value from an asynchronous request'. Everything you want to do with valuePage you should do inside the done callback.

Upvotes: 4

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