change variable outside of xhr.onload function

Accepted Answer

An async request will continue immediately after send() to your return statement, so return authorized will return whatever it's set to initially. Your onload handler will get called long after the function has returned.

What you'll need to do is provide a callback that can be called in your onload (or onerror) handler to alert your app to the status of the request.

In theory a synchronous request is possible, but if I remember right, at least one of iPhone or Android doesn't support it (properly, at least). It's good practice not to block on a network request, anyway, since you have no idea how long it will take and your app/UI will be completely unresponsive in the interim.

— answered April 4th 2011 by K T
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2 Comments

good suggestion, I just tried that but its having the same effect.

request.onload = function(){
    callback(this.responseText); 
}

function callback(response){
    // JSON encoded server return
    var json = JSON.parse(response);

    if(json.status == 'success'){
        // Update authorized variable to true
        authorized = true;
    } else {
        authorized = false;
    }
}

If I misunderstood please clarify.

Thanks!

— commented April 4th 2011 by Josey Morton

A little, maybe.

I assume what you had originally was something like:

function myAuthorizationFunction()
{
    ...
    result = myNS.user.createSession(...);
    // Now handle result appropriately
    ...
}

The problem as pointed out is that you have no idea when the async request will return from the wilds of the internet; it shoots off the request.send() and your program continues on its merry way without pausing.

What you need to do is move the logic for handling the authorization result into a callback function, so instead of a linear myAuthorizationFunction, you have something more like:

function onAuthorizationResult(result)
{
    // Now handle result appropriately
    ...
}

function myAuthorizationFunction()
{
    ...
    myNS.user.createSession(..., onAuthorizationResult);  // extra callback argument
}

Then you'll have:

myNS.user.createSession = function(..., onResult)

and your request.onload will contain something like:

if(json.status == 'success'){
    // Update authorized variable to true
    authorized = true;
} else {
    authorized = false;
}
onResult(authorized);  // to actually tell the application about the authorization

— commented April 4th 2011 by K T

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2 Answers

Accepted Answer