JSDoc
Why code documentation?
Forms of code documentation
What "data" should be?

JSDoc annotations for function parameters

Real-time hints in Visual Studio Code
@author
@return (or @returns)
Function which returns a number:
Some of the more popular annotation tags:
Generating the docs
npm init -y
npm i jsdoc --save-dev
node_modules/jsdoc/jsdoc.js app.js
Documentation in HTML
Useful Links
Thanks for your attention