I have a text entry area on my site where the user can enter text. I’m wanting to run some javascript every time a user enters a new character in the text field. This will enable me to assess what the user is typing as they type it and ensure it meets certain rules.
I cannot test this just yet . But you can use jQuery to bind to the textarea do a google for. “textarea on change event”
Where you will find many answers using it
Update.
Check the on() http://api.jquery.com/on/