VectorScrolling rewrite for 2020. Only 350bytes Gzipped

vs.js

/*
Copyright 2020 Aaron Sherrill

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and 
associated documentation files (the "Software"), to deal in the Software without restriction, 
including without limitation the rights to use, copy, modify, merge, publish, distribute, 
sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is 
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial 
portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT
LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. 
IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION 
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

var _vs = function(){
  
	var clamp = function (val, min, max) {
		return val > max ? max : val < min ? min : val;
	}
	
	var scale = function(num, in_min, in_max, out_min, out_max) {
		let n = (num - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
		return clamp(n, out_min, out_max);
	}
	
	function calculatePositions(){
		for(var i = 0, vector, rect, a, b, offsetPerc; i < _vs.prototype.vectors.length; i++) {
			vector = _vs.prototype.vectors[i];
			rect = vector.element.getBoundingClientRect();
			a = (window.innerHeight * vector.options[1]) - (rect.height * vector.options[0]);
			b = (window.innerHeight * vector.options[3]) - (rect.height * vector.options[2]);
			offsetPerc = scale(rect.top, a, b, 0, 1);
			vector.callback(offsetPerc);
		}
	}
	
  window.addEventListener("resize", calculatePositions);
  
	return {
		onScroll: function() {
			requestAnimationFrame(function(){
				calculatePositions()
			});
		},
		add: function(element, options, callback) {
			var id = Math.random().toString(36).substring(2, 15) + Math.random().toString(36).substring(2, 15);
			_vs.prototype.vectors.push({
				element: element,
				options: options,
				callback: callback,
				id: id
			});
			calculatePositions();
			return id;
		},
		remove: function(id) {
			for(var i = 0; i <= _vs.prototype.vectors.length; i++) {
				if(_vs.prototype.vectors[i].id == id) {
					_vs.prototype.vectors.splice(i, 1);
					break;
				}	
			}
		}
	}
}
_vs.prototype.vectors = [];
var vs = new _vs();