How to change a label's contents using Javascript?

I have a label that holds a value and a text box into which I will enter a number. I have another label, which should dynamically give the difference between the two as I type the number in the text box. How do I do this using Javascript? I tried:

<script type="text/javascript">
function compute_diff(){
    var lbl1 = document.getElementById("<%=label1.ClientID%>").value;
    var txtbox = document.getElementById("<%=textbox1.ClientID%>").value;
    var lbl2value = lbl1 - txtbox
    document.getElementById("<%=label2.ClientID%>").innerText = lbl2value;
    return true;
    }
</script>

I am calling this function on the OnKeyUp event, but it is not 开发者_JAVA百科firing it. What is the correct way of going about this? I am developing the site using ASP.Net.

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The line

var lbl2value = lbl1 - txtbox

will not work. You will need to use a string diff algorithm such as the one at

http://ejohn.org/projects/javascript-diff-algorithm/

In addition, consider using jQuery to ensure that this works cross browser as the implementation of innerText can differ from browser to browser.