Question

Possible Duplicate:
How to return the response from an AJAX call from a function?

I have a function that reads numerical data from a file online. While the file is retrieved correctly (proven by the value displayed by the alert), when I try to set it to output and then return output, I get an undefined result.

I tried to go through scoping tutorials to no avail. What am I doing wrong?

function readFileFromWeb() {
    var output;

    jQuery.get('http://domain.com', function(data) {
        alert(data);
        output = data;
    });

    return output;
}

Answer 1

Here’s how it should be done, via a callback function.

function readFileFromWeb(callback) {
    jQuery.get('http://domain.com', function(data) {
        callback && callback(data);
    });
}

// ...

readFileFromWeb(function (data) {
    alert(data);
});

This is because jQuery.get is an asynchronous function i.e. it doesn’t block while executing and thus returns immediately. And that is infact the reason why the jQuery.get function requires a callback function, so that it fires your callback function once the AJAX query has returned.

Thus, you will need to use the same callback pattern when implementing your own readFileFromWeb function.