Question

I have an condition which has to hold before and after an XMLHttpRequest usage, but not during. Example:

var running = false; // condition

function go (callback)
{
    running = true; // condition broken

    var http = new XMLHttpRequest ();
    http .open ("GET", url, true);
    http .onreadystatechange = function ()
    {
        if (4 == this .readyState)
        {
            try
            {
                callback (this .responseText);
            }
            catch (e) {}

            running = false; // condition restored
        }
    }
}

I need to guarantee that running will always eventually become false, regardless of how the XMLHttpRequest plays out.

Is this sufficient or do I need to check some other eventualities?

Answer 1

It looks like that this check is enough (http://www.w3.org/TR/XMLHttpRequest/). readyState is 4 if the data transfer has been completed or something went wrong during the transfer.

Make sure you set some reasonable value for timeout (the default is 0, that is no timeout).