Question

I’m kinda new on javascript, and I’ve having difficulties (for 2 days now) in implementing the following:

Consider I have an Object(), ‘engine’, which I want it to respond differently according to a post’s content. I.e. there is an action by the user, the engine interprets the action, sends a request to the server, and server responds, and the ‘engine’ acts accordingly.

As a minimal example of the desired behavior, I present an ‘engine’ which hypothetically is receiving mouse click’s position (receiveClickEvent), sends it trough a ‘post’ (requestByAsyncPost), and responds according to its content (respondToRequest):

A small function for doing the post

function requestByAsyncPost(content, funct)
{
/* some initialization missing here to not confuse the reader */
xmlhttp.onreadystatechange = function()
    {
        if (xmlhttp.readyState==4 && xmlhttp.status==200)
        {
            funct(xmlhttp.response);
        }
    }
xmlhttp.open("POST","foobar.php", true);
xmlhttp.setRequestHeader("Content-type","application/x-www-form-urlencoded");
xmlhttp.send(content);
}

var engine = new Object()
engine.respondToRequest = function(content) {/*implementation*/ }

a small piece of code which I want to be activated when a mouse click occurs (doesn’t matter now how it is triggered)

engine.receiveClickEvent = function(position)
{
    var funct = function(content)
    {
         this.respondToRequest(content); //<<<---- I want to refer engine's 'this'
    }
    requestByAsyncPost('request=click&position=['+position[0]+','+position[1]+')', funct);
}

This is not working the way I want because the “this” is inside the function funct. How can I implement this kind of behavior?

Answer 1

You must remember outer this by this way or other. Like:

engine.receiveClickEvent = function(position)
{
    var self = this;
    var funct = function(content)
    {
         self.respondToRequest(content); //<<<---- 'self' refers engine's 'this'
    }; // <<<--- btw, missed semicolon
    requestByAsyncPost('request=click&position=['+position[0]+','+position[1]+')', funct);
}; // <<<--- btw, here, too :-)