Detecting immediate text entry in text box

I have created a form in HTML, which consists of a text box. Is there a javascript command/function which detects as soon as an entry has gone into the text box (eg onChange???), so I can then immediately call up a function to read and react to that entry?

Thanks.

you can use onChange or onBlur.Attach these to the textbox itself.

Thanks Acidic, but there's still a problem with my situation. Your solution works well when the user manually types his whole string into the text box, then text-input detection happens when the user takes the focus away from the text box.

The situation is this. The text in the text box is not directly user-entered. The user makes some selection and a Javascript function writes the approriate text into the text-box. I need to detect as soon as text enters the box, not after the user has focussed away from the box.

Hope you can help.

Thanks.

Since modifying the text via JavaScript doesn't trigger key events, there's no way to do this except modifying the script that writes in the box.