Onchange actions for custom entry fields

Hello,

I am currently creating custom functionality within expressionengine to be able to cross-reference entry data with data from an external api

I created a custom field that will accept the id of the entity from the external api that the entry corresponds to

What I want to do is create an onchange event on my custom entry field that will accept a search term and run a search query against the external api and show an active list of results to choose from (like google search)

When the user clicks an entry in the list, I want the field to populate with the corresponding id

I have lots of experience with web development, and I already know how to handle all of the JS, but I am very new to EE and, after looking at the hooks documentation, I’m not really sure where I can add an event listener in an elegant fashion.

Maybe one of you EE-savvy folks can point me in the right direction?

Also, I would like to know where I can add script tags to the control panel’s header.

Any help is greatly appreciated.

Thanks -D