How disable all suggestions in a language in Monaco, and only keep mine using registerCompletionItemProvider

I’m creating a custom language that will be like Javascript, with less functions in it. I want only my custom completions to be displayed.

Can I disable all existing completions items in javascript ? (I don’t want to totally disable items because mine would disappear)

Another option would be to create a custom language, but I will lose all javascript formatting. I’m only using Javascript, no other framework.