A simplified, modern version of the original smooth scroll.

import animateScroll from './path/smooth-scroll.js';

const a = document.getElementById('link');
const destination = document.getElementById('destination');

a.addEventListener('click', e => {
	animateScroll(destination, {speed: 5000});
	e.preventDefault();
});

This version, compared to the original, is:

• it's 50% smaller
• it's an ES6 module
• it uses requestAnimationFrame instead of setInterval
• it doesn't include polyfills (closest, Object.assign / extend). If you really need them, include them yourself.
• it doesn't escape characters from hash (no CSS.escape)
• includes only two easing options (easeOutCubic, easeInCubic) instead of 12. If you need a different one, pass a function as an easing param.
• it doesn't track or measure your header. If you need it, measure it yourself and pass to the SmoothScroll via the offset param (you can also pass a function here).

The code is available under the MIT License.