Problem - Watch for active input boxes in a page and trigger events if specific words are entered into the input box

Steps

1. Click 'reply or reply all'
2. Input box becomes active
3. Enter |intro
4. |intro text gets replaced with long form version. The |intro is like a snippet or short code

Heres what I'm thinking

1. Query all input boxes on a page
2. Check for input with focus
3. Add event listener on input to check for keyup events
4. Conditional statement to check if string contains specific snippet/short code
5. If condition is met then replace snippet with long form text

What do you think of my approach to this functonality