Develop Reference

P5.js game crashes due to TypeError for a missing element in an array

OK, so I run into this problem where my program regularly crashes mid-game due to a TypeError: Uncaught TypeError: bullets[i] is undefined
The error occurs in the function where I check for every variable in the bullets and the enemies array if there is a collision.
This is the Source Code of this small school project I created, and I've been trying to troubleshoot this particular bug for hours at a time now. If anyone were able to help me that would be amazing as I can't quite grasp what the problem could be other than their occurring a collision when an element has already been spliced. But since the draw() function in P5.js runs 60 times per second that shouldn't really happen as regularly as it does, so I don't understand how this even can be an issue.
function setup() {
createCanvas(displayWidth - 20, displayHeight - 20);
angleMode(DEGREES);
rectMode(CENTER);
ellipseMode(CENTER);
playerX = width / 2;
playerY = height / 2;
}
let playerX = 0;
let playerY = 0;
let angle = 0;
let timer = 120;
let time = 0;
let v = 2;
let cooldown = 20;
let color = 50;
let hit = 0;
var bullets = [];
var enemies_easy = [];
var enemies_hard = [];
var score = 0;
var highscore = 0;
var gameover = false;
var gamestarted = false;
var nexthard = 5;
var currentenemy = 0;
function draw() {
if (!gamestarted) {
push();
textAlign(CENTER);
background('black');
translate(displayWidth / 2, displayHeight / 2);
textSize(width / 50);
fill('white');
text('Welcome!', 0, -100);
text('Controls:', 0, 0);
text('Fullscreen: F Moving: W, A, S, D Restart: R Shooting: Left Mouse Button Start: Space Bar', 0, 100);
pop();
if (keyIsDown(32)) {
bullets = [];
gamestarted = true;
}
} else {
if (!gameover) {
//calculates shot enemies_easy
bulletcollision();
//shoots if weapon cooldown is expired
background('black');
cooldown--;
activategun();
//draw hero
angle = atan2(mouseY - playerY, mouseX - playerX) + 90;
push();
fill('blue');
translate(playerX, playerY);
rotate(angle);
ellipse(0, 0, 40, 40);
//draw gun
fill('grey');
rect(0, 0 - 25, 10, 20);
pop();
//move hero
move();
//creates enemies with increasing difficulty
time++;
difficulty();
spawnenemy_easy();
spawnenemy_hard();
//shows score on screen
showscore();
//draw crosshair
noCursor();
push();
fill('white');
stroke('white');
line(mouseX, mouseY, mouseX + 20, mouseY);
line(mouseX, mouseY, mouseX - 20, mouseY);
line(mouseX, mouseY, mouseX, mouseY + 20);
line(mouseX, mouseY, mouseX, mouseY - 20);
pop();
//checks for game over
playercollision();
} else {
if (keyIsDown(82)) {
bullets = [];
enemies_easy = [];
enemies_hard = [];
timer = 120;
time = 0;
cooldown = 20;
score = 0;
playerX = width / 2;
playerY = height / 2;
v = 2;
gameover = false;
}
}
}
}
class bullet {
constructor() {
this.x = playerX;
this.y = playerY;
this.angle = createVector(mouseX - playerX, mouseY - playerY);
this.angle.normalize();
}
drawbullet() {
push();
fill('white');
ellipse(this.x, this.y, 10, 10);
pop();
this.y = this.y + 10 * this.angle.y;
this.x = this.x + 10 * this.angle.x;
}
}
class enemy_easy {
constructor() {
this.x = random(-1000, width + 1000);
if (this.x > width || this.x < 0) {
if (this.x > width) {
this.x = width;
this.y = random(0, height + 1);
}
if (this.x < 0) {
this.x = 0;
this.y = random(0, height + 1);
} else {}
} else {
let i = floor(random(0, 2));
this.y = i * height;
}
}
drawenemy_easy() {
push();
this.angle = createVector(this.x - playerX, this.y - playerY);
this.angle.normalize();
fill('red');
ellipse(this.x, this.y, 30, 30);
rotate(angle);
pop();
this.x = this.x - v * this.angle.x; // * random(0, 5);
this.y = this.y - v * this.angle.y; // * random(0, 5);
}
}
class enemy_hard {
constructor() {
this.x = random(-1000, width + 1000);
if (this.x > width || this.x < 0) {
if (this.x > width) {
this.x = width;
this.y = random(0, height + 1);
}
if (this.x < 0) {
this.x = 0;
this.y = random(0, height + 1);
} else {}
} else {
let i = floor(random(0, 2));
this.y = i * height;
}
}
drawenemy_hard() {
push();
this.angle = createVector(this.x - playerX, this.y - playerY);
this.angle.normalize();
fill('purple');
ellipse(this.x, this.y, 30, 30);
rotate(angle);
pop();
this.x = this.x - v * this.angle.x; // * random(0, 5);
this.y = this.y - v * this.angle.y; // * random(0, 5);
}
}
function keyPressed() {
//fullscreen Taste F: https://www.geeksforgeeks.org/p5-js-fullscreen-function/
if (keyCode === 70) {
let fs = fullscreen();
fullscreen(!fs);
}
}
function move() {
if (keyIsDown(83) && playerY <= height - 22) {
playerY = playerY + 4;
}
if (keyIsDown(87) && playerY >= 22) {
playerY = playerY - 4;
}
if (keyIsDown(68) && playerX <= width - 22) {
playerX = playerX + 4;
}
if (keyIsDown(65) && playerX >= 22) {
playerX = playerX - 4;
}
}
function activategun() {
for (var i = 0; i < bullets.length; i++) {
bullets[i].drawbullet();
if (bullets[i].x <= 0 || bullets[i].y <= 0 || bullets[i].x >= width || bullets[i].y >= height) {
bullets.splice(i, 1);
}
}
}
function mousePressed() {
if (cooldown < 0) {
bullets.push(new bullet());
cooldown = 20;
}
}
function spawnenemy_easy() {
for (var i = 0; i < enemies_easy.length; i++) {
enemies_easy[i].drawenemy_easy();
}
}
function spawnenemy_hard() {
for (var i = 0; i < enemies_hard.length; i++) {
enemies_hard[i].drawenemy_hard();
}
}
function newenemy() {
if (currentenemy < nexthard) {
enemies_easy.push(new enemy_easy());
currentenemy++;
} else {
enemies_hard.push(new enemy_hard());
currentenemy = 0;
nexthard = random(2, 6);
}
}
function bulletcollision() {
for (var i = 0; i < bullets.length; i++) {
for (var e = 0; e < enemies_easy.length; e++) {
var distance = createVector(bullets[i].x - enemies_easy[e].x, bullets[i].y - enemies_easy[e].y);
if (distance.mag() <= 18) {
bullets.splice(i, 1);
enemies_easy.splice(e, 1);
score++;
if (score > highscore) {
highscore++;
}
}
}
for (var e = 0; e < enemies_hard.length; e++) {
var distance = createVector(bullets[i].x - enemies_hard[e].x, bullets[i].y - enemies_hard[e].y);
if (distance.mag() <= 18) {
bullets.splice(i, 1);
hit++;
if (hit == 2) {
enemies_hard.splice(e, 1);
score++;
if (score > highscore) {
highscore++;
}
hit = 0;
}
}
}
}
}
function playercollision() {
for (var i = 0; i < enemies_easy.length; i++) {
var distance = createVector(enemies_easy[i].x - playerX, enemies_easy[i].y - playerY);
if (distance.mag() <= 25) {
push();
background(abs(255 * sin(random(0, 255))), 255 * sin(random(0, 255)), 255 * sin(random(0, 255)));
fill('white');
textAlign(CENTER);
textSize(width / 40);
translate(width / 2, height / 2);
text("Game Over!", 0, -100);
text("Score: " + score, 0, 0);
text("High Score: " + highscore, 0, 100);
pop();
return gameover = true;
}
}
for (var i = 0; i < enemies_hard.length; i++) {
var distance = createVector(enemies_hard[i].x - playerX, enemies_hard[i].y - playerY);
if (distance.mag() <= 25) {
push();
background(abs(255 * sin(random(0, 255))), 255 * sin(random(0, 255)), 255 * sin(random(0, 255)));
fill('white');
textAlign(CENTER);
textSize(width / 40);
translate(width / 2, height / 2);
text("Game Over!", 0, -100);
text("Score: " + score, 0, 0);
text("High Score: " + highscore, 0, 100);
pop();
return gameover = true;
}
}
}
function difficulty() {
if (time >= timer) {
newenemy();
time = 0;
timer = timer * 0.99;
v = v * 1.02;
}
}
function showscore() {
push();
fill('white');
textSize(width / 55);
textAlign(CENTER);
text('Score: ' + score, 100, 100);
pop();
}
Does anyone know how I could fix this issue or if I even can?
Any help is appreciated!

The problem is that you are removing bullets from the array as you iterate through the array. Use while-loop instead of the for-loop:
function bulletcollision() {
let i = 0;
while (i < bullets.length) {
let bullet_hit = false;
for (var e = 0; e < enemies_easy.length; e++) {
var distance = createVector(bullets[i].x - enemies_easy[e].x, bullets[i].y - enemies_easy[e].y);
if (distance.mag() <= 18) {
bullet_hit = true;
destroy_enemy(enemies_easy, e);
}
}
for (var e = 0; e < enemies_hard.length; e++) {
var distance = createVector(bullets[i].x - enemies_hard[e].x, bullets[i].y - enemies_hard[e].y);
if (distance.mag() <= 18) {
bullet_hit = true;
hit++;
if (hit == 2) {
destroy_enemy(enemies_hard, e);
hit = 0;
}
}
}
if (bullet_hit) {
bullets.splice(i, 1);
} else {
i ++;
}
}
}
function destroy_enemy(enemies, e) {
enemies.splice(e, 1);
score++;
highscore = Math.max(highscore, score);
}
See also Looping through array and removing items, without breaking for loop.

Unexpected Result when Resolving Collision in JavaScript

I've been making a simple game just with the HTML5 canvas and plain JavaScript. Most recently I tried adding a feature to shoot bullets which would then destroy obstacles but I've come upon a problem. Whenever you shoot a bullet it doesn't move until another is shot. Even when it starts moving and collides with one of the obstacles nothing happens. I've done some troubleshooting and I can't seem to get to the bottom of it. Any help and/or suggestions would be greatly appreciated.
Collision handling code:
for(var i = 0; i < this.bullets.length - 1; i++) { // -1 is present because whenever I remove it I get an error. I have a feeling this may be related to the order of how everything updates, will be fixed
this.bullets[i].x += this.bullets[i].speed;
if(this.bullets[i].x > cvs.width) {
this.bullets.splice(i, 1);
}
for(var j = 0; j < obstacles.length - 1; j++) { // Same here
if(rectanglesColliding(this.bullets[i], obstacles[j])) {
console.log("Collision");
}
}
}
Full player object:
var player = {
score: 0,
x: 50,
y: 150,
radius: 10,
jumping: false,
bullets: [],
velocityX: 0,
velocityY: 1,
angle: 90,
update: function() {
this.draw();
this.score++;
if(this.y + this.radius + 2 > cvs.height - 50 && this.jumping === false || this.y - this.radius + 2 < 0 + 50 && this.jumping === true) {
this.velocityY = 0;
} else if(this.jumping === false){
this.velocityY = 4;
} else {
this.velocityY = -4;
}
obstacles.forEach((obstacle) => {
if(colliding(this, obstacle)) {
gameEnded = true;
}
});
this.x += this.velocityX;
this.y += this.velocityY;
for(var i = 0; i < this.bullets.length - 1; i++) { // -1 is present because whenever I remove it I get an error. I have a feeling this may be related to the order of how everything updates, will be fixed
this.bullets[i].x += this.bullets[i].speed;
if(this.bullets[i].x > cvs.width) {
this.bullets.splice(i, 1);
}
for(var j = 0; j < obstacles.length - 1; j++) { // Same here
if(rectanglesColliding(this.bullets[i], obstacles[j])) {
console.log("Collision");
}
}
}
},
draw: function() {
this.bullets.forEach((bullet) => {
ctx.fillStyle = 'green';
ctx.fillRect(bullet.x, bullet.y, 7, 2);
});
ctx.fillStyle = 'blue';
ctx.beginPath();
ctx.arc(this.x, this.y, this.radius, 0, 2 * Math.PI);
ctx.fill();
}
};
Collision Detection Function:
function rectanglesColliding(rect1, rect2) {
if(rect1.x < rect2.x + rect2.width &&
rect1.x + rect1.width > rect2.x && // Found on Mozilla.com: https://developer.mozilla.org/en-US/docs/Games/Techniques/2D_collision_detection
rect1.y < rect2.y + rect2.height &&
rect1.y + rect1.height > rect2.y) return true;
else return false;
}
Shoot Function:
function shoot() {
player.bullets.push({ x: player.x + 10, y: player.y, speed: 6 });
}
Object of the game:
Survive as long as you can by avoiding the obstacles.
Controls:
Space: Go up
W: Shoot Bullet
Full code snippet:
var cvs = document.getElementById('canvas');
var ctx = cvs.getContext("2d");
var gameEnded = false;
var player = {
score: 0,
x: 50,
y: 150,
radius: 10,
jumping: false,
bullets: [],
velocityX: 0,
velocityY: 1,
angle: 90,
update: function() {
this.draw();
this.score++;
if(this.y + this.radius + 2 > cvs.height - 50 && this.jumping === false || this.y - this.radius + 2 < 0 + 50 && this.jumping === true) {
this.velocityY = 0;
} else if(this.jumping === false){
this.velocityY = 4;
} else {
this.velocityY = -4;
}
obstacles.forEach((obstacle) => {
if(colliding(this, obstacle)) {
gameEnded = true;
}
});
this.x += this.velocityX;
this.y += this.velocityY;
for(var i = 0; i < this.bullets.length - 1; i++) {
this.bullets[i].x += this.bullets[i].speed;
if(this.bullets[i].x > cvs.width) {
this.bullets.splice(i, 1);
}
for(var j = 0; j < obstacles.length - 1; j++) {
if(rectanglesColliding(this.bullets[i], obstacles[j])) {
console.log("Collision");
// obstacles.splice(i, 1);
}
}
}
},
draw: function() {
this.bullets.forEach((bullet) => {
ctx.fillStyle = 'green';
ctx.fillRect(bullet.x, bullet.y, 7, 2);
});
ctx.fillStyle = 'blue';
ctx.beginPath();
ctx.arc(this.x, this.y, this.radius, 0, 2 * Math.PI);
ctx.fill();
}
};
var obstacles = [{ x: 150, y: 60, width: 10, height: 20 }];
document.addEventListener('keydown', (event) => {
if(event.key === ' ') {
player.jumping = true;
}
if(event.key === 'w') {
shoot();
}
});
document.addEventListener('keyup', (event) => {
if(event.key === ' ') {
player.jumping = false;
}
});
function randomIntFromRange(min, max) {
return Math.floor(Math.random() * (max - min + 1) + min);
}
function getWidth() {
return Math.max(
document.body.scrollWidth,
document.documentElement.scrollWidth,
document.body.offsetWidth,
document.documentElement.offsetWidth,
document.documentElement.clientWidth
);
}
function getHeight() {
return Math.max(
document.body.scrollHeight,
document.documentElement.scrollHeight,
document.body.offsetHeight,
document.documentElement.offsetHeight,
document.documentElement.clientHeight
);
}
function colliding(circle, rect) {
var distX = Math.abs(circle.x - rect.x - rect.width / 2);
var distY = Math.abs(circle.y - rect.y - rect.height / 2);
if(distX > (rect.width / 2 + circle.radius)) return false;
if(distY > (rect.height / 2 + circle.radius)) return false;
if(distX <= (rect.width / 2)) return true;
if(distY <= (rect.height / 2)) return true;
}
function rectanglesColliding(rect1, rect2) {
if(rect1.x < rect2.x + rect2.width &&
rect1.x + rect1.width > rect2.x &&
rect1.y < rect2.y + rect2.height &&
rect1.y + rect1.height > rect2.y) {
return true;
}
}
function distance(x1, y1, x2, y2) {
const xDist = x2 - x1;
const yDist = y2 - y1;
return Math.sqrt(Math.pow(xDist, 2) + Math.pow(yDist, 2));
}
function shoot() {
player.bullets.push({ x: player.x + 10, y: player.y, speed: 6 });
}
function generateObstacle() {
var obstacle = {
x: obstacles[0].x + randomIntFromRange(cvs.width - 100, cvs.width + 70),
y: 0 + randomIntFromRange(20, 550),
width: randomIntFromRange(25, 35),
height: randomIntFromRange(10, 25)
};
for(var i = 0; i < obstacles.length; i++) {
if(distance(obstacle.x, obstacle.y, obstacles[i].x, obstacles[i].y) < 65) {
obstacle = {
x: obstacles[0].x + randomIntFromRange(cvs.width - 100, cvs.width + 70),
y: 0 + randomIntFromRange(20, 550),
width: randomIntFromRange(25, 35),
height: randomIntFromRange(10, 25)
};
i = -1;
}
}
obstacles.push({ x: obstacle.x, y: obstacle.y, width: obstacle.width, height: obstacle.height });
}
function removeBadObstacles() {
for(var i = 0; i < obstacles.length; i++) {
if(obstacles[i].x < 0) {
obstacles.splice(i, 1);
}
}
}
function updateObstacles() {
if(obstacles[obstacles.length - 1].x < cvs.width + 5) {
generateObstacle();
generateObstacle();
}
obstacles.forEach((obstacle) => {
obstacle.x -= 10;
ctx.fillStyle = 'red';
ctx.fillRect(obstacle.x, obstacle.y, obstacle.width, obstacle.height);
});
}
function init() {
cvs.width = getWidth();
cvs.height = getHeight();
update();
}
function update() {
if(gameEnded) {
ctx.font = '50px Verdana';
return ctx.fillText('Game Over', 110, cvs.height / 2);
}
requestAnimationFrame(update);
removeBadObstacles();
ctx.fillStyle = 'black';
ctx.fillRect(0, 0, cvs.width, cvs.height);
updateObstacles();
player.update();
ctx.font = '30px Impact';
ctx.fillText("Score: " + player.score, 20, 40);
}
init();
<!DOCTYPE html>
<html>
<head>
<title>Game</title>
</head>
<body>
<canvas id="canvas"></canvas>
<script type="text/javascript" src="./JS/main.js"></script>
</body>
</html>

when iterate through a array, the last item is at length-1 (which mean you should use < length, not < length-1)
the remove code should be obstacles.splice(j, 1); (i is the index for bullet)
you do not assign size to bullet (and you may also want to use this size when draw)
var cvs = document.getElementById('canvas');
var ctx = cvs.getContext("2d");
var gameEnded = false;
var player = {
score: 0,
x: 50,
y: 150,
radius: 10,
jumping: false,
bullets: [],
velocityX: 0,
velocityY: 1,
angle: 90,
update: function() {
this.draw();
this.score++;
if(this.y + this.radius + 2 > cvs.height - 50 && this.jumping === false || this.y - this.radius + 2 < 0 + 50 && this.jumping === true) {
this.velocityY = 0;
} else if(this.jumping === false){
this.velocityY = 4;
} else {
this.velocityY = -4;
}
obstacles.forEach((obstacle) => {
if(colliding(this, obstacle)) {
gameEnded = true;
}
});
this.x += this.velocityX;
this.y += this.velocityY;
for(var i = 0; i < this.bullets.length; i++) {//<==============
this.bullets[i].x += this.bullets[i].speed;
if(this.bullets[i].x > cvs.width) {
this.bullets.splice(i, 1);
}
for(var j = 0; j < obstacles.length; j++) {//<==============
if(rectanglesColliding(this.bullets[i], obstacles[j])) {
console.log("Collision");
obstacles.splice(j, 1);//<==============
}
}
}
},
draw: function() {
this.bullets.forEach((bullet) => {
ctx.fillStyle = 'green';
ctx.fillRect(bullet.x, bullet.y, 7, 2);
});
ctx.fillStyle = 'blue';
ctx.beginPath();
ctx.arc(this.x, this.y, this.radius, 0, 2 * Math.PI);
ctx.fill();
}
};
var obstacles = [{ x: 150, y: 60, width: 10, height: 20 }];
document.addEventListener('keydown', (event) => {
if(event.key === ' ') {
player.jumping = true;
}
if(event.key === 'w') {
shoot();
}
});
document.addEventListener('keyup', (event) => {
if(event.key === ' ') {
player.jumping = false;
}
});
function randomIntFromRange(min, max) {
return Math.floor(Math.random() * (max - min + 1) + min);
}
function getWidth() {
return Math.max(
document.body.scrollWidth,
document.documentElement.scrollWidth,
document.body.offsetWidth,
document.documentElement.offsetWidth,
document.documentElement.clientWidth
);
}
function getHeight() {
return Math.max(
document.body.scrollHeight,
document.documentElement.scrollHeight,
document.body.offsetHeight,
document.documentElement.offsetHeight,
document.documentElement.clientHeight
);
}
function colliding(circle, rect) {
var distX = Math.abs(circle.x - rect.x - rect.width / 2);
var distY = Math.abs(circle.y - rect.y - rect.height / 2);
if(distX > (rect.width / 2 + circle.radius)) return false;
if(distY > (rect.height / 2 + circle.radius)) return false;
if(distX <= (rect.width / 2)) return true;
if(distY <= (rect.height / 2)) return true;
}
function rectanglesColliding(rect1, rect2) {
if(rect1.x < rect2.x + rect2.width &&
rect1.x + rect1.width > rect2.x &&
rect1.y < rect2.y + rect2.height &&
rect1.y + rect1.height > rect2.y) {
return true;
}
}
function distance(x1, y1, x2, y2) {
const xDist = x2 - x1;
const yDist = y2 - y1;
return Math.sqrt(Math.pow(xDist, 2) + Math.pow(yDist, 2));
}
function shoot() {
player.bullets.push({ x: player.x + 10, y: player.y, speed: 6, width: 7, height: 6 }); //<====================
}
function generateObstacle() {
var obstacle = {
x: obstacles[0].x + randomIntFromRange(cvs.width - 100, cvs.width + 70),
y: 0 + randomIntFromRange(20, 550),
width: randomIntFromRange(25, 35),
height: randomIntFromRange(10, 25)
};
for(var i = 0; i < obstacles.length; i++) {
if(distance(obstacle.x, obstacle.y, obstacles[i].x, obstacles[i].y) < 65) {
obstacle = {
x: obstacles[0].x + randomIntFromRange(cvs.width - 100, cvs.width + 70),
y: 0 + randomIntFromRange(20, 550),
width: randomIntFromRange(25, 35),
height: randomIntFromRange(10, 25)
};
i = -1;
}
}
obstacles.push({ x: obstacle.x, y: obstacle.y, width: obstacle.width, height: obstacle.height });
}
function removeBadObstacles() {
for(var i = 0; i < obstacles.length; i++) {
if(obstacles[i].x < 0) {
obstacles.splice(i, 1);
}
}
}
function updateObstacles() {
if(obstacles[obstacles.length - 1].x < cvs.width + 5) {
generateObstacle();
generateObstacle();
}
obstacles.forEach((obstacle) => {
obstacle.x -= 10;
ctx.fillStyle = 'red';
ctx.fillRect(obstacle.x, obstacle.y, obstacle.width, obstacle.height);
});
}
function init() {
cvs.width = getWidth();
cvs.height = getHeight();
update();
}
function update() {
if(gameEnded) {
ctx.font = '50px Verdana';
return ctx.fillText('Game Over', 110, cvs.height / 2);
}
requestAnimationFrame(update);
removeBadObstacles();
ctx.fillStyle = 'black';
ctx.fillRect(0, 0, cvs.width, cvs.height);
updateObstacles();
player.update();
ctx.font = '30px Impact';
ctx.fillText("Score: " + player.score, 20, 40);
}
init();
<!DOCTYPE html>
<html>
<head>
<title>Game</title>
</head>
<body>
<canvas id="canvas"></canvas>
<script type="text/javascript" src="./JS/main.js"></script>
</body>
</html>

snake game crashes after eating several times with TypeError variable undefined

It's been few days that I've been learning JavaScript. So I'm completely new to this.
This is my code for snake game and it isn't complete yet but I've run into a problem. I'm not completely sure that if it's a logical error or not.
After eating the food several times, the game crashes with
TypeError: snakeBody[l] is undefined.
Screenshot of the error is here.
The entire code is given below:
<!DOCTYPE html>
<html lang="en">
<head>
<style>
canvas {
background: #080d16;
border: 5px solid green;
padding: 0;
}
</style>
</head>
<body>
<canvas id="mycan" class="mycan" width="1860" height="920"></canvas>
<script>
var canvas = document.getElementById('mycan');
var ctx = canvas.getContext('2d');
var snakeSize = 20;
var snakeX = 100;
var snakeY = 100;
var foodX = 310;
var foodY = 310;
var foodSize = 10;
var dx = 20;
var dy = 20;
var leftPressed = false;
var rightPressed = true;
var topPressed = false;
var bottomPressed = false;
var snakeBody = [{x:snakeX,y:snakeY},{x:snakeX-20,y:snakeY}];
var z = 0;
//keypress event listner
document.addEventListener('keypress', keyHandler, false);
//keypress event handler function
function keyHandler(e) {
if (e.keyCode == 37) {
leftPressed = true;
rightPressed = false;
topPressed = false;
bottomPressed = false;
} else if (e.keyCode == 38) {
leftPressed = false;
rightPressed = false;
topPressed = true;
bottomPressed = false;
} else if (e.keyCode == 39) {
leftPressed = false;
rightPressed = true;
topPressed = false;
bottomPressed = false;
} else if (e.keyCode == 40) {
leftPressed = false;
rightPressed = false;
topPressed = false;
bottomPressed = true;
}
}
//draw food
function food() {
ctx.beginPath();
ctx.arc(foodX, foodY, foodSize, 0, Math.PI * 2);
ctx.fillStyle = "pink";
ctx.fill();
ctx.closePath();
}
//draw snake
function snake() {
for (var l = 0; l < snakeBody.length; l++) {
ctx.beginPath();
ctx.rect(snakeBody[l].x, snakeBody[l].y, snakeSize, snakeSize);
if (l == 0) {
ctx.fillStyle = "lightblue";
} else {
ctx.fillStyle = 'grey';
}
ctx.fill();
ctx.closePath();
}
console.log(l);
var head = {
x: snakeX,
y: snakeY
};
snakeBody.pop();
snakeBody.unshift(head);
}
function tail() {
if ((snakeX + dx / 2 > foodX - foodSize && snakeX + dx / 2 < foodX + foodSize) && (snakeY + dy / 2 > foodY - foodSize && snakeY + dy / 2 < foodY + foodSize)) {
foodX = (Math.floor(Math.random() * 88) + 1) * 20 + 10;
foodY = (Math.floor(Math.random() * 45) + 1) * 20 + 10;
z++;
if (snakeBody[snakeBody.length - 1].x == snakeBody[snakeBody.length - 2].x && snakeBody[0].y < snakeBody[1].y) {
snakeBody[z] = {
x: snakeBody[snakeBody.length - 1].x,
y: snakeBody[snakeBody.length - 1].y + 20
};
} else if (snakeBody[snakeBody.length - 1].x == snakeBody[snakeBody.length - 2].x && snakeBody[0].y > snakeBody[1].y) {
snakeBody[z] = {
x: snakeBody[snakeBody.length - 1].x,
y: snakeBody[snakeBody.length - 1].y - 20
};
} else if (snakeBody[snakeBody.length - 1].y == snakeBody[snakeBody.length - 2].y && snakeBody[0].x > snakeBody[1].x) {
snakeBody[z] = {
x: snakeBody[snakeBody.length - 1].x - 20,
y: snakeBody[snakeBody.length - 1].y
};
} else if (snakeBody[snakeBody.length - 1].y == snakeBody[snakeBody.length - 2].y && snakeBody[0].x < snakeBody[1].x) {
snakeBody[z] = {
x: snakeBody[snakeBody.length - 1].x + 20,
y: snakeBody[snakeBody.length - 1].y
};
}
}
}
function draw() {
ctx.clearRect(0, 0, canvas.width, canvas.height);
snake();
food();
tail();
if (rightPressed && snakeX + dx < canvas.width) {
snakeX += dx;
} else if (leftPressed && snakeX > 0) {
snakeX += -dx;
} else if (topPressed && snakeY > 0) {
snakeY += -dy;
} else if (bottomPressed && snakeY + dy < canvas.height) {
snakeY += dy;
}
}
setInterval(draw, 80);
</script>
</body>
</html>

You have error in algorithm - your snakeBody put/pops elements and you miss some "corner cases" when use indexes in this array - the problem is not with JS but with algorithm - debug it and also use "triangle" in chrome konsole on left side of error to see more details (stacktrace)

I check and run your code more than once. This error does not appear for me. It is good for you to check the values in snake function and then use them. Modify your snake function to this
function snake() {
for (var l = 0; l < snakeBody.length; l++) {
ctx.beginPath();
if(snakeBody && snakeBody[l] && snakeBody[l].hasOwnProperty('x') && snakeBody[l].hasOwnProperty('y')) {
ctx.rect(snakeBody[l].x, snakeBody[l].y, snakeSize, snakeSize);
}
if (l == 0) {
ctx.fillStyle = "lightblue";
} else {
ctx.fillStyle = 'grey';
}
ctx.fill();
ctx.closePath();
}
console.log(l);
var head = {
x: snakeX,
y: snakeY
};
snakeBody.pop();
snakeBody.unshift(head);
}
As you can see, snakeBody has no indexes 24 and 25. But this condition satisfy this.

Canvas Rectangle & Ball Collision Not working

I'm making a html5 canvas game and I have a problem with the collision.
The problem is when the ball collides with any platform, the ball gravity should be -1 and go up as the same velocity as the platforms but it only works with the last platform and the left one. How can I fix it? Thanks!
HTML:
<html>
<head>
<title>Falldown</title>
</head>
<body>
<canvas id="canvas" width = "380" height= "640"></canvas>
<script src="beta.js"></script>
</body>
</html>
JS Code:
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var isMenu = true;
var isPlaying = false;
var testing = true;
var pressingLeft = false;
var pressingRight = false;
var Platforms = [];
var difficulty = 1;
var gravity = 1;
var Player = {
color: "red",
radius: 7.5,
stepY: 1.5,
x: 175,
y: 75
};
function RectCircleColliding(circle, rect) {
var distX = Math.abs(circle.x - rect.x - rect.width / 2);
var distY = Math.abs(circle.y - rect.y - 20 / 2);
if (distX > (rect.width / 2 + circle.radius)) return false;
if (distY > (20 / 2 + circle.radius)) return false;
if (distX <= (rect.width / 2)) return true;
if (distY <= (20 / 2)) return true;
var dx = distX - rect.width / 2;
var dy = distY - 20 / 2;
return (dx * dx + dy * dy <= (circle.radius * circle.radius));
}
function drawBackground() {
ctx.fillStyle = "black";
ctx.fillRect(0, 0, canvas.width, canvas.height);
if (isMenu && !isPlaying) {
createText("60px monospace", "white", "FallDown", 45, 130);
createText("34px Arial", "white", "PLAY", 130, 260);
createText("34px Arial", "white", "LEADERBOARD", 50, 340);
createText("34px Arial", "white", "SETTINGS", 90, 420);
} else {
if (testing) {
Platforms = [];
for (var i = 0; i < 13; i++) {
Platforms.push({
"x": 10,
"y": 160 + (i * 70),
"width": (Math.random() * canvas.width) - 60
});
}
testing = false;
}
for (var i in Platforms) {
ctx.fillStyle = "#00ffff";
ctx.fillRect(10, Platforms[i].y, Platforms[i].width, 20);
var totalTest = Platforms[i].width + 60;
ctx.fillRect(totalTest + 30, Platforms[i].y, canvas.width - totalTest, 20);
Platforms[i].y -= 1;
if (RectCircleColliding(Player, Platforms[i])) {
gravity = -1;
} else {
gravity = 1;
}
}
detectBorderCollision();
detectPlayerCollision();
drawPlayer();
drawBorder();
if (Platforms.length === 7) Platforms = [];
}
}
function detectBorderCollision() {
if (Player.x > 370 - Player.radius) {
Player.x = 370 - Player.radius;
} else if (Player.x < 3.8 + Player.radius * 2) {
Player.x = 3.8 + Player.radius * 2
}
}
function detectPlayerCollision() {
}
function drawPlayer() {
ctx.beginPath();
ctx.fillStyle = Player.color;
ctx.arc(Player.x, Player.y, Player.radius, 0, 2 * Math.PI);
ctx.fill();
ctx.closePath();
Player.y += gravity;
if (pressingRight) {
Player.x += 2;
} else if (pressingLeft) {
Player.x -= 2;
}
/*
ctx.fillStyle = "#00ffff";
ctx.fillRect(10, 160, 300, 20);
*/
}
function drawBorder() {
ctx.beginPath();
ctx.strokeStyle = "#00ffff";
ctx.lineWidth = 10;
ctx.moveTo(5, 0);
ctx.lineTo(5, 640);
ctx.moveTo(375, 0);
ctx.lineTo(375, 640);
ctx.stroke();
ctx.closePath();
}
function createText(font, color, value, posX, posY) {
ctx.font = font;
ctx.fillStyle = color;
ctx.fillText(value, posX, posY)
}
function isInside(realX, realY, x1, x2, y1, y2) {
return (realX > x1 && realX < x2) && (realY > y1 && realY < y2)
}
function drawGame() {
drawBackground();
}
function startDrawing() {
ctx.clearRect(0, 0, canvas.width, canvas.height);
drawGame();
requestAnimationFrame(startDrawing);
}
function Init() {
requestAnimationFrame(startDrawing);
canvas.addEventListener("click", function(evt) {
var rect = canvas.getBoundingClientRect();
var mouseX = evt.clientX - rect.left;
var mouseY = evt.clientY - rect.top;
if (isMenu && !isPlaying) {
if (isInside(mouseX, mouseY, 115, 230, 220, 270)) {
isPlaying = true;
isMenu = false;
} else if (isInside(mouseX, mouseY, 35, 320, 300, 345)) {
console.log("Leaderboard");
} else if (isInside(mouseX, mouseY, 75, 270, 380, 430)) {
console.log("Settings");
}
}
});
window.addEventListener("keydown", function(evt) {
if (!isMenu && isPlaying) {
if (evt.keyCode === 39) { // right
pressingRight = true;
} else if (evt.keyCode === 37) { // left
pressingLeft = true;
}
}
});
window.addEventListener("keyup", function(evt) {
if (!isMenu && isPlaying) {
if (evt.keyCode === 39) { // right
pressingRight = false;
} else if (evt.keyCode === 37) { // left
pressingLeft = false;
}
}
});
}
Init();

There are so many magic numbers in your code that debugging it is difficult and tedious. Replace all the number literals with identifiers which describe what the values represent.
The following amendment to part of the drawBackground function causes all the collisions with left hand platforms to work, but not perfectly.
var hasCollided;
for (var i in Platforms) {
ctx.fillStyle = "#00ffff";
ctx.fillRect(10, Platforms[i].y, Platforms[i].width, 20);
var totalTest = Platforms[i].width + 60;
ctx.fillRect(totalTest + 30, Platforms[i].y, canvas.width - totalTest, 20);
Platforms[i].y -= 1;
if (!hasCollided) {
if (RectCircleColliding(Player, Platforms[i])) {
gravity = -1;
hasCollided = true;
} else {
gravity = 1;
}
}
}

Duplicate randomly multiple objects inside a javascript for loop

I found this platform game on the Internet and I modified it a bit:
<canvas id="canvas" widht=1000 height=400></canvas>
<script>
(function () {
var requestAnimationFrame = window.requestAnimationFrame || window.mozRequestAnimationFrame || window.webkitRequestAnimationFrame || window.msRequestAnimationFrame;
window.requestAnimationFrame = requestAnimationFrame;
})();
var canvas = document.getElementById("canvas"),
ctx = canvas.getContext("2d"),
width = 1000,
height = 400,
player = {
x: width / 2,
y: height - 15,
width: 5,
height: 5,
speed: 3,
velX: 0,
velY: 0,
jumping: false,
grounded: false
},
keys = [],
friction = 0.8,
gravity = 0.3;
var boxes = [];
// dimensions
a = Math.floor((Math.random() * 20) + 1);
for (i = 0; i < a; i++) {
random1 = Math.floor((Math.random() * 1000) + 1);
random2 = Math.floor((Math.random() * 400) + 1);
random3 = Math.floor((Math.random() * 200) + 1);
random4 = Math.floor((Math.random() * 200) + 1);
boxes.push({
x: random1,
y: random2,
width: random3,
height: random4
}
boxes.push({
x: 0,
y: 0,
width: 10,
height: height
});
boxes.push({
x: 0,
y: height - 2,
width: width,
height: 50
});
boxes.push({
x: width - 10,
y: 0,
width: 50,
height: height
});
canvas.width = width;
canvas.height = height;
function update() {
// check keys
if (keys[38] || keys[32]) {
// up arrow or space
if (!player.jumping && player.grounded) {
player.jumping = true;
player.grounded = false;
player.velY = -player.speed * 2;
}
}
if (keys[39]) {
// right arrow
if (player.velX < player.speed) {
player.velX++;
}
}
if (keys[37]) {
// left arrow
if (player.velX > -player.speed) {
player.velX--;
}
}
player.velX *= friction;
player.velY += gravity;
ctx.clearRect(0, 0, width, height);
ctx.fillStyle = "black";
ctx.beginPath();
player.grounded = false;
for (var i = 0; i < boxes.length; i++) {
ctx.rect(boxes[i].x, boxes[i].y, boxes[i].width, boxes[i].height);
var dir = colCheck(player, boxes[i]);
if (dir === "l" || dir === "r") {
player.velX = 0;
player.jumping = false;
} else if (dir === "b") {
player.grounded = true;
player.jumping = false;
} else if (dir === "t") {
player.velY *= -1;
}
}
if(player.grounded){
player.velY = 0;
}
player.x += player.velX;
player.y += player.velY;
ctx.fill();
ctx.fillStyle = "red";
ctx.fillRect(player.x, player.y, player.width, player.height);
requestAnimationFrame(update);
}
function colCheck(shapeA, shapeB) {
// get the vectors to check against
var vX = (shapeA.x + (shapeA.width / 2)) - (shapeB.x + (shapeB.width / 2)),
vY = (shapeA.y + (shapeA.height / 2)) - (shapeB.y + (shapeB.height / 2)),
// add the half widths and half heights of the objects
hWidths = (shapeA.width / 2) + (shapeB.width / 2),
hHeights = (shapeA.height / 2) + (shapeB.height / 2),
colDir = null;
// if the x and y vector are less than the half width or half height, they we must be inside the object, causing a collision
if (Math.abs(vX) < hWidths && Math.abs(vY) < hHeights) {
// figures out on which side we are colliding (top, bottom, left, or right)
var oX = hWidths - Math.abs(vX),
oY = hHeights - Math.abs(vY);
if (oX >= oY) {
if (vY > 0) {
colDir = "t";
shapeA.y += oY;
} else {
colDir = "b";
shapeA.y -= oY;
}
} else {
if (vX > 0) {
colDir = "l";
shapeA.x += oX;
} else {
colDir = "r";
shapeA.x -= oX;
}
}
}
return colDir;
}
document.body.addEventListener("keydown", function (e) {
keys[e.keyCode] = true;
});
document.body.addEventListener("keyup", function (e) {
keys[e.keyCode] = false;
});
window.addEventListener("load", function () {
update();
});
</script>
The problem is in the for loop when I want to create multiple boxes with random width, height, position but that didn't work. How could I do that?

In you code there are two syntax error. first one is you didn't close for loop and second one is inside for loop first push operation was not close properly.
i have update code.
(function () {
var requestAnimationFrame = window.requestAnimationFrame || window.mozRequestAnimationFrame || window.webkitRequestAnimationFrame || window.msRequestAnimationFrame;
window.requestAnimationFrame = requestAnimationFrame;
})();
var canvas = document.getElementById("canvas"),
ctx = canvas.getContext("2d"),
width = 1000,
height = 400,
player = {
x: width / 2,
y: height - 15,
width: 5,
height: 5,
speed: 3,
velX: 0,
velY: 0,
jumping: false,
grounded: false
},
keys = [],
friction = 0.8,
gravity = 0.3;
var boxes = [];
// dimensions
a = Math.floor((Math.random() * 20) + 1);
for (i = 0; i < a; i++) {
random1 = Math.floor((Math.random() * 1000) + 1);
random2 = Math.floor((Math.random() * 400) + 1);
random3 = Math.floor((Math.random() * 200) + 1);
random4 = Math.floor((Math.random() * 200) + 1);
boxes.push({
x: random1,
y: random2,
width: random3,
height: random4
});
boxes.push({
x: 0,
y: 0,
width: 10,
height: height
});
boxes.push({
x: 0,
y: height - 2,
width: width,
height: 50
});
boxes.push({
x: width - 10,
y: 0,
width: 50,
height: height
});
canvas.width = width;
canvas.height = height;
}
function update() {
// check keys
if (keys[38] || keys[32]) {
// up arrow or space
if (!player.jumping && player.grounded) {
player.jumping = true;
player.grounded = false;
player.velY = -player.speed * 2;
}
}
if (keys[39]) {
// right arrow
if (player.velX < player.speed) {
player.velX++;
}
}
if (keys[37]) {
// left arrow
if (player.velX > -player.speed) {
player.velX--;
}
}
player.velX *= friction;
player.velY += gravity;
ctx.clearRect(0, 0, width, height);
ctx.fillStyle = "black";
ctx.beginPath();
player.grounded = false;
for (var i = 0; i < boxes.length; i++) {
ctx.rect(boxes[i].x, boxes[i].y, boxes[i].width, boxes[i].height);
var dir = colCheck(player, boxes[i]);
if (dir === "l" || dir === "r") {
player.velX = 0;
player.jumping = false;
} else if (dir === "b") {
player.grounded = true;
player.jumping = false;
} else if (dir === "t") {
player.velY *= -1;
}
}
if(player.grounded){
player.velY = 0;
}
player.x += player.velX;
player.y += player.velY;
ctx.fill();
ctx.fillStyle = "red";
ctx.fillRect(player.x, player.y, player.width, player.height);
requestAnimationFrame(update);
}
function colCheck(shapeA, shapeB) {
// get the vectors to check against
var vX = (shapeA.x + (shapeA.width / 2)) - (shapeB.x + (shapeB.width / 2)),
vY = (shapeA.y + (shapeA.height / 2)) - (shapeB.y + (shapeB.height / 2)),
// add the half widths and half heights of the objects
hWidths = (shapeA.width / 2) + (shapeB.width / 2),
hHeights = (shapeA.height / 2) + (shapeB.height / 2),
colDir = null;
// if the x and y vector are less than the half width or half height, they we must be inside the object, causing a collision
if (Math.abs(vX) < hWidths && Math.abs(vY) < hHeights) {
// figures out on which side we are colliding (top, bottom, left, or right)
var oX = hWidths - Math.abs(vX),
oY = hHeights - Math.abs(vY);
if (oX >= oY) {
if (vY > 0) {
colDir = "t";
shapeA.y += oY;
} else {
colDir = "b";
shapeA.y -= oY;
}
} else {
if (vX > 0) {
colDir = "l";
shapeA.x += oX;
} else {
colDir = "r";
shapeA.x -= oX;
}
}
}
return colDir;
}
document.body.addEventListener("keydown", function (e) {
keys[e.keyCode] = true;
});
document.body.addEventListener("keyup", function (e) {
keys[e.keyCode] = false;
});
window.addEventListener("load", function () {
update();
});
<canvas id="canvas" widht=1000 height=400></canvas>