VS Code Intellisense works for .ts files but not for .js files

I am using firebase functions.
VScode doesn’t show me errors and suggestions for .js files, but if I change the extension to .ts it works! I don’t use TypeScript for my project.

Also, I use it alongside JavaScript for hosting and Intellisense works well!

I don’t know, what’s wrong?

>Solution :

You need to set up a jsconfig.json file. For how to do so, see the following:

• https://code.visualstudio.com/docs/languages/jsconfig
• What is jsconfig.json?