Ending an Event Driven Function in JavaScript
<p>I am using JavaScript with HTML5.  When the user clicks on a button, an event-driven JavaScript function starts up.  When the user clicks on the button again, another instance of this function starts up. So I have two instances of the same function handling a event.  However I only want the new instance to be running.  How do I end the first instance of the?</p>

<p>An example is a function with the following code</p>

<pre><code>Canvas.paper = Raphael(xOffset,yOffset,imageWidth,imageHeight);
masterBackground = Canvas.paper.rect(0,0,imageWidth,imageHeight);

window.onkeydown=function(e){
    // Event handler code
}

document.addEventListener('keydown', function(event) {
    // Event handler code
}

masterBackground.mousemove(function(e){
    // Event handler code
}
</code></pre>
