Question

Suppose I had the following function:

function alertMesg()
{
   alert("This ok function alerts message!");
}

Now at run time I would like to change the alertMesg function to do something else. My thought was to do somehting like this.

var temp = window.alertMesg.toString.replace("ok","great")
temp = temp.replace('function alertMesg()',"");
window.alertMesg = new Function(temp);

Basically, the problem is I have no control over the source in the alertMesg function. I would like to change the function, but I can’t actually change the source of it because it is produced server side. That being said, I need it to act differently.

PS: I forgot to mention an important part: I have to keep most of the function. I can’t just replace the function out right. I have to keep 95% of the function the way it is, and change the other five percent.

@Barlow Tucker, quixoto, pekka
Thanks, for the interest.

Basically, I don’t think the proxy idea will work because I am not just adding functionality, I am changing the functionality of the code. I want for example, the third line of the function to be different. In my real life example I have to add a line right in the middle of a function.

Answer 1

If you must replace the content of a function, it is possible:

function alertMesg()
{
   alert ("This ok function alerts my message!");
}

alertMesg(); // alerts "This ok function alerts my message!"

// do whatever you want to the function here
var temp = alertMesg.toString();
temp = temp.replace('my', 'your');

// now replace the original function
alertMesg=new Function(temp.substring(temp.indexOf('{')+1,temp.lastIndexOf('}')));

alertMesg(); // alerts "This ok function alerts your message!"

This probably isn’t the best way to do what you’re trying to achieve, but I can’t really suggest anything else unless you provide more details.