Using functions of multiple javascript files


How can I make use of functions from other js files in the index.js/main.js file?


Atom uses NodeJS (v7.9.0 as of writing this; can check with atom -v). So you would use require("path/to/file"). Here is a guide for it

Alternatively, using the "use babel"; directive, you can use import <name> from <module> syntax from ES6. More on this is best found in the docs