Acceleration Based Scroll Position

ScrollPos.js

const MOUSE_WHEEL_EVENT = "wheel";
const TOUCH_MOVE = "touchmove";
const TOUCH_END = "touchend";
const MOUSE_DOWN = "mousedown";
const MOUSE_UP = "mouseup";
const MOUSE_MOVE = "mousemove";
class ScrollPos {
	constructor() {
		this.acceleration = 0;
		this.maxAcceleration = 5;
		this.maxSpeed = 20;
		this.velocity = 0;
		this.dampen = 0.97;
		this.speed = 8;
		this.touchSpeed = 8;
		this.scrollPos = 0;
		this.velocityThreshold = 1;
		this.snapToTarget = false;
		this.mouseDown = false;
		this.lastDelta = 0;
		
		window.addEventListener(MOUSE_WHEEL_EVENT, event => {
			event.preventDefault();
			this.accelerate(Math.sign(event.deltaY) * this.speed);
		});
		
		window.addEventListener(TOUCH_MOVE, event => {
			//event.preventDefault();
			let delta = this.lastDelta-event.targetTouches[0].clientY;
			this.accelerate(Math.sign(delta) * this.touchSpeed);
			this.lastDelta = event.targetTouches[0].clientY;
		})
		
		window.addEventListener(TOUCH_END, event =>{
			this.lastDelta = 0;
		})
		
		window.addEventListener(MOUSE_DOWN, event=>{
			this.mouseDown = true;
		})
		
		window.addEventListener(MOUSE_MOVE, event=>{
			if(this.mouseDown){
				let delta = this.lastDelta-event.clientY;
				this.accelerate(Math.sign(delta) * this.touchSpeed*0.4);
				this.lastDelta = event.clientY;
			}
		})
		
		window.addEventListener(MOUSE_UP, event=>{
			this.lastDelta = 0;
			this.mouseDown = false;
		})

	}
	accelerate(amount) {
		if (this.acceleration < this.maxAcceleration) {
			this.acceleration += amount;
		}
	}
	update() {
		this.velocity += this.acceleration;
		if (Math.abs(this.velocity) > this.velocityThreshold) {
			this.velocity *= this.dampen;
			this.scrollPos += this.velocity;
		} else {
			this.velocity = 0;
		}
		if (Math.abs(this.velocity) > this.maxSpeed) {
			this.velocity = Math.sign(this.velocity) * this.maxSpeed;
		}
		this.acceleration = 0;
	}
	snap (snapTarget, dampenThreshold = 100, velocityThresholdOffset = 1.5) {
		if(Math.abs(snapTarget - this.scrollPos) < dampenThreshold) {
			this.velocity *= this.dampen;
		}
		if (Math.abs(this.velocity) < this.velocityThreshold+velocityThresholdOffset) {
			this.scrollPos += (snapTarget - this.scrollPos) * 0.1;
		}
	}
	project(steps = 1) {
		if(steps === 1)	return this.scrollPos + this.velocity * this.dampen
		var scrollPos = this.scrollPos;
		var velocity = this.velocity;

		for(var i = 0; i < steps; i++) {
				velocity *= this.dampen;
				scrollPos += velocity;
		}
		return scrollPos;
	}
}