nextStep 
Steps an integer by a specified amount (+ or -), within a range from 0 to max, wrapping when the new value exceeds the range.
Install
$ npm install @andersaloof/next-step
Why?
Having made similar logic in a dozen of slideshows/galleries over the years, handling previous and next buttons to increase/decrease a current index, it was time to move it out to a separate module.
Usage
nextStep(current, max, value)
Example code
const nextStep = require('@andersaloof/next-step');
const nextValue = nextStep(1, 5, 2); // Increase current value 1 by 2, returns 3;
const anotherValue = nextStep(1, 5, -3); // Decrease current value 1 by -3, with a max value of 5, returns 4;License
MIT. See LICENSE.md for details.