how to make this ground platform initial starting position to be drawn from the beginning of execution on whole canvas width? also, add player spawn position at left-top corner.: class Platform {
constructor(x, y, w, h) {
this.x = x;
this.y = y;
this.w = w;
this.h = h;
}
collidesWith(obj) {
if (obj.y + obj.h <= this.y) return false;
if (obj.y >= this.y + this.h) return false;
if (obj.x + obj.w <= this.x) return false;
if (obj.x >= this.x + this.w) return false;
const objAbove = obj.y + obj.h - obj.vy <= this.y;
const objBelow = obj.y - obj.vy >= this.y + this.h;
const objLeft = obj.x + obj.w - obj.vx <= this.x;
const objRight = obj.x - obj.vx >= this.x + this.w;
if (obj.vy > 0 && objAbove && !objBelow) {
obj.y = this.y - obj.h;
obj.vy = 0;
obj.jumping = false;
return true;
}
if (obj.vy < 0 && !objAbove && objBelow) {
obj.y = this.y + this.h;
obj.vy = 0;
return true;
}
if (obj.vx < 0 && objRight) {
obj.x = this.x + this.w;
obj.vx = 0;
return true;
}
if (obj.vx > 0 && objLeft) {
obj.x = this.x - obj.w;
obj.vx = 0;
return true;
}
return false;
}
}
class GroundPlatform extends Platform {
constructor(x, y, w, h) {
super(x, y, w, h);
}
}
class Player {
constructor(x, y, w, h) {
this.x = x;
this.y = y;
this.w = w;
this.h = h;
this.vx = 0;
this.vy = 0;
this.jumping = false;
}
move(keys) {
const friction = .8;
const gty = 0.8;
if (keys[87] && !this.jumping) {
this.vy -= 10;
this.jumping = true;
}
if (keys[68]) {
this.vx += 0.8;
}
if (keys[65]) {
this.vx -= 0.8;
}
this.vx *= friction;
this.vy += gty;
this.x += this.vx;
this.y += this.vy;
if (this.x < 0) {
this.x = 0;
}
if (this.y < 0) {
this.y = 0;
}
if (this.x + this.w > canvas.width) {
this.x = canvas.width - this.w;
this.vx = 0;
}
if (this.y + this.h > canvas.height) {
this.y = canvas.height - this.h;
this.vy = 0;
this.jumping = false;
}
}
}

class Projectile {
constructor(x, y, vx, vy) {
this.x = x;
this.y = y;
this.vx = vx;
this.vy = vy;
this.radius = 3;
this.color = "red";
}
update() {
this.x += this.vx;
this.y += this.vy;
}
draw(ctx) {
ctx.beginPath();
ctx.arc(this.x, this.y, this.radius, 0, 2 * Math.PI);
ctx.fillStyle = this.color;
ctx.fill();
}
}



class Entity {
constructor() {
this.x = canvas.width;
this.y = Math.random() * canvas.height;
this.w = 10;
this.h = 10;  

this.vy = 0;
this.jumping = false;
this.projectiles = [];
this.color = "blue";


}
jump() {
if (!this.jumping) {
this.vy -= 25 - Math.random() * 25;
this.jumping = true;
}
}
update(platforms) {
for (let i = 0; i < platforms.length; i++) {
platforms[i].collidesWith(this);
}
const friction = .99;
const gty = 1;
this.vx = friction;
this.vy += gty;
this.x += this.vx;
this.y += this.vy;this.period = Math.PI;
this.minVx = -2 + Math.sin(Math.random() * 2 * Math.PI) * 2;
this.maxVx = -5 + Math.cos(Math.random() * 2 * Math.PI) * -10;
  this.vx = this.vxForce = randomRange(this.minVx, this.maxVx);
    const t = performance.now() / 1000;
    const wave = Math.sin(t * Math.PI / this.period);
  this.vxForce = lerp(this.maxVx, this.minVx, (wave + 5) / 200, 10); 
  this.x += this.vxForce;      
if (Math.random() < .01) {
this.projectiles.push(new Projectile(this.x, this.y, -2 - Math.random() * 6, -2 + Math.random() * 8));
}
for (let i = 0; i < this.projectiles.length; i++) {
this.projectiles[i].update();
if (this.projectiles[i].x < 0 || this.projectiles[i].y < 0 || this.projectiles[i].x > canvas.width || this.projectiles[i].y > canvas.height) {
this.projectiles.splice(i, 1);
i;
}
}
if (Math.random() < .01) {
this.jump();
}
}
draw(ctx) {
ctx.fillStyle = this.color;
ctx.fillRect(this.x, this.y, this.w, this.h);
for (let i = 0; i < this.projectiles.length; i++) {
this.projectiles[i].draw(ctx);
}
}
}

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

function lerp(a, b, t, d) {
  return a * (1 - t / d) + b * t / d;
}

class Game {
constructor(canvas) {
this.canvas = canvas;
this.ctx = canvas.getContext("2d");
this.platforms = [];
this.player = new Player(10, 10, 10, 10);
this.scrollSpeed = 2;
this.entities = [];
this.entitySpawnRate = .1;
this.entitySpawnTimer = 1;
this.entityIncreaseFactor = .1;
this.keys = {};
  for (let i = 0; i < 10; i++) {
this.createRandomPlatform();
}
document.addEventListener("keydown", evt => {
this.keys[evt.keyCode] = true;
});
document.addEventListener("keyup", evt => {
delete this.keys[evt.keyCode];
});
requestAnimationFrame(this.update.bind(this));
}
createRandomPlatform() {
const groundHeight = 5;
const x = this.canvas.width;
const y = Math.random() * (this.canvas.height - 10 * groundHeight);
const w = 20 + Math.random() * 50;
const h = 5;
this.platforms.push(new Platform(x, y, w, h));
}
createGroundPlatform() {
  const x = this.canvas.width;
  const y = this.canvas.height - 50;
  const w = 100 + Math.random() * 50;
  const h = 20;
  this.platforms.push(new Platform(x, y, w, h));
}
update() {
this.player.move(this.keys);
for (let i = 0; i < this.platforms.length; i++) {
this.platforms[i].collidesWith(this.player);
this.platforms[i].x -= this.scrollSpeed;
}
for (let i = 0; i < this.entities.length; i++) {
if (this.entities[i]) {
this.entities[i].update(this.platforms);
if (this.entities[i].x < 0) {
this.entities.splice(i, 1);
i;
for (let j = 0; j < this.entityIncreaseFactor; j++) {
this.entities.push(new Entity());
}
} else {
for (let j = 0; j < this.entities[i].projectiles.length; j++) {
if (this.entities[i].projectiles[j].x > this.player.x && this.entities[i].projectiles[j].x < this.player.x + this.player.w && this.entities[i].projectiles[j].y > this.player.y && this.entities[i].projectiles[j].y < this.player.y + this.player.h) {
this.player.vy -= 20;
this.player.jumping = true;
this.entities[i].projectiles.splice(j, 1);
j;
}
}
this.entities[i].draw(this.ctx);
}
}
}
this.player.x -= this.scrollSpeed;
if (this.platforms[this.platforms.length - 1].x < this.canvas.width - 100) {
  this.createRandomPlatform();
  this.createGroundPlatform();
}
this.entitySpawnTimer++;
if (this.entitySpawnTimer >= 60 / this.entitySpawnRate) {
this.entitySpawnTimer = 0;
this.entities.push(new Entity());
this.entitySpawnRate += .001;
this.entityIncreaseFactor = Math.min(this.entityIncreaseFactor + .001, .001);
}
this.ctx.clearRect(0, 0, this.canvas.width, this.canvas.height);
for (let i = 0; i < this.platforms.length; i++) {
let p = this.platforms[i];
this.ctx.fillRect(p.x, p.y, p.w, p.h);
}
for (let i = 0; i < this.entities.length; i++) {
this.entities[i].draw(this.ctx);
}
this.ctx.fillRect(this.player.x, this.player.y, this.player.w, this.player.h);
requestAnimationFrame(this.update.bind(this));
}
}

let canvas = document.createElement("canvas");
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
document.body.appendChild(canvas);
new Game(canvas);