Do you need to use the results of a search to send to an API for validation? I'm still not understanding what exactly you're trying to accomplish and what the workflow is. If so, you could probably handle this with a custom search command.
You can absolutely use Javascript to call an API. The bigger question is if you need to use credentials to authenticate with the API. It also sounds like you're not familiar with coding in Javascript so that's going to be the biggest barrier. To call a REST API in javascript, look at jQuery's ajax.
https://api.jquery.com/jquery.ajax/
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