Question

How would one make a javascript function which constantly checks to see if the user has input data into one or more textboxes?
Thanks!

Answer 1

You shouldn’t use setInterval. You should use onchange event.

See http://jsfiddle.net/QwBU8/

document.getElementById('myinput').onchange=change;
document.getElementById('mytextarea').onchange=change;
function change(e){
    if(!e){e=window.event;}
    document.getElementById('log').innerHTML+='Element with id "'+this.id+'" has changed\n';  
}

But be aware that this event isn’t fired at the moment that the textbox is modified; it is fired when it loses focus (only if it has changed, of course).

If you want to fire the event each time is modified you can use oninput (but it’s not supported by all browsers).

But avoid using setInterval, it eats up a lot of resources. Imagine that you have 30 tabs opened in your browser, and all of them have a different setInterval. The browser will freeze!!