Ball.js

const INITIAL_VELCOTIY = 0.025
const VELOCITY_INCREASE = 0.000005

export default class Ball {
    constructor(ballElem) {
        this.ballElem = ballElem
        this.reset()
    }

    get x() {
        return parseFloat(getComputedStyle(this.ballElem).getPropertyValue("--x"))
    }

    set x(val) {
        this.ballElem.style.setProperty("--x", val)
    }

    get y() {
        return parseFloat(getComputedStyle(this.ballElem).getPropertyValue("--y"))
    }

    set y(val) {
        this.ballElem.style.setProperty("--y", val)
    }

    rect() {
        return this.ballElem.getBoundingClientRect()
    }

    update(delta, paddleRects) {
        this.x += this.direction.x * this.velocity * delta
        this.y += this.direction.y * this.velocity * delta
        this.velocity += VELOCITY_INCREASE * delta
        const rect = this.rect()

        if(rect.bottom >= window.innerHeight || rect.top <= 0) {
            this.direction.y *= -1
        }
        if(paddleRects.some(r => isCollision(r, rect))) {
            this.direction.x *= -1
        }
    }

    reset() {
        this.x = 50
        this.y = 50
        this.direction = {x: 0}
        while(Math.abs(this.direction.x <= 0.2) || Math.abs(this.direction.x > 0.9)) {
            const heading = randomNumberBetween(0, 2 * Math.PI)
            this.direction = {x: Math.cos(heading), y: Math.sin(heading)}
        }
        this.velocity = INITIAL_VELCOTIY
    }
}

function isCollision(rect1, rect2) {
    return (rect1.left <= rect2.right && rect1.right >= rect2.left && rect1.top <= rect2.bottom && rect1.bottom >= rect2.top)
}

function randomNumberBetween(min, max) {
    return Math.random() * (max-min) + min
}