It took me a while to figure out how to monitor the input text changes in a text box. I created kyepress and mousedown and various other event handlers to start the process to monitor the input text box. It worked in some cases, but failed in others.
In the end, I have to take a look into the source code that implemented Autocomplete control released with Ajax Contrl Took Kit by Microsoft. The correct answer is to intercept focus, blur, and keydown events. In the past, it would not be possible because all the software is not open-sourced. The only solution is to read documentation and use trial and error approach.