Search only partial textField rawValue

My form has a textField that users enter part numbers separated by commas. I want to write an if statement that looks to see if one of the part numbers is included in the list. Is there a way to script to search for only part of a textField's rawValue or formattedValue?

So if the rawValue of textField1 is 1234, 4569, 3582

I want to be able to enter 4569 in textField2 (a different textField)  and click a button that runs a script to see if 4569 is included in the list of part numbers.

Is this possible?

Also: is it possible to send the comma separated part numbers to a list box?

I appreciate any help provided.