Since JavaScript is loosely coupled, providing a working autocomplete solution is not as easy as for statically typed languages like Java. Your best bets with Atom are the following packages:

• autocomplete-plus - this is now bundled with Atom as the default autocomplete provider
• ternjs - this looks pretty good, but requires some configuration.

I suggest you give these a try.

I think you should go for atom-ternjs

This is java script intelligence for atom

You need to change(Enable) setting for atom-ternjs

1. Use autocomplete-snippets
2. Display both autocomplete-snippets and function name

and many more depends on your requirements ...

If you are using modern JavaScript or TypeScript or Node then atom-typescript is good. It uses tsserver (like vscode) which gives autocomplete, go to definition, syntax checking and other ide goodies. By default it's not enabled for JavaScript. Follow the docs to enable for .js files - https://github.com/TypeStrong/atom-typescript/blob/master/docs/faq.md#i-want-to-use-atom-typescript-with-javascript-too. Configuration for tsserver is done by .jsconfig file - https://code.visualstudio.com/docs/languages/jsconfig.