Question

I have a aspx page with about 200 textboxes with onkeyup events that some users have complained is really slow.

Would having all of those onkeyup events cause this slowness?

Answer 1

Probably. I’m guessing you have 1 keyup event handler / listener per textarea. Instead use event delegation; register the keyup listener on the document and determine the element that it was triggered on using event.target or event.srcElement.

document.onkeyup = function(e){
    e = e || window.event;
    var textarea = e.target || e.srcElement;    // reference to the textarea
}