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<div class="container">
<header>
<div class="contrast">100%</div>
<div class="score">0</div>
</header>
<div class="grid"></div>
<footer>Press an arrow key or space to start!
<div>Ready for hard more? Press H
</footer>
</div>
<a id="youtube" href="https://youtu.be/TAmYp4jKWoM" target="_top">
<span>See how this game was made</span>
</a>
<div id="youtube-card">
How to create a snake game with JavaScript
</div>
html,
body {
height: 100%;
margin: 0;
}
body {
--size: 15px;
--color: black;
font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
color: var(--color);
background-color: #ff8585;
background: linear-gradient(
162deg,
rgba(255, 133, 133, 1) 0%,
rgba(227, 84, 95, 1) 100%
);
}
footer {
font-size: 0.8em;
}
@media (min-height: 425px) {
body {
--size: 25px;
}
footer {
height: 40px;
font-size: 1em;
}
}
.container {
display: flex;
flex-direction: column;
justify-content: center;
align-items: center;
height: 100%;
}
header {
display: flex;
justify-content: space-between;
width: calc(var(--size) * 17);
font-size: 2em;
font-weight: 900;
}
.grid {
display: grid;
grid-template-columns: repeat(15, auto);
grid-template-rows: repeat(15, auto);
border: var(--size) solid var(--color);
}
.tile {
position: relative;
width: var(--size);
height: var(--size);
}
.content {
position: absolute;
width: 100%;
height: 100%;
}
footer {
margin-top: 20px;
max-width: calc(var(--size) * 17);
text-align: center;
}
footer a:visited {
color: inherit;
}
#youtube,
#youtube-card {
display: none;
}
@media (min-height: 425px) {
/** Youtube logo by https://codepen.io/alvaromontoro */
#youtube {
z-index: 2;
display: block;
width: 100px;
height: 70px;
position: absolute;
bottom: 20px;
right: 20px;
background: white;
border-radius: 50% / 11%;
transform: scale(0.8);
transition: transform 0.5s;
}
#youtube:hover,
#youtube:focus {
transform: scale(0.9);
background: red;
}
#youtube::before {
content: "";
display: block;
position: absolute;
top: 7.5%;
left: -6%;
width: 112%;
height: 85%;
background: white;
border-radius: 9% / 50%;
}
#youtube:hover::before,
#youtube:focus::before {
background: red;
}
#youtube::after {
content: "";
display: block;
position: absolute;
top: 20px;
left: 40px;
width: 45px;
height: 30px;
border: 15px solid transparent;
box-sizing: border-box;
border-left: 30px solid #ff8585;
}
#youtube:hover::after,
#youtube:focus::after {
border-left: 30px solid white;
}
#youtube span {
font-size: 0;
position: absolute;
width: 0;
height: 0;
overflow: hidden;
}
#youtube:hover + #youtube-card {
display: block;
position: absolute;
bottom: 12px;
right: 10px;
padding: 25px 130px 25px 25px;
width: 300px;
background-color: white;
}
}
/*
If you want to learn how this game was made, check out this video, that walks through the main ideas:
YouTube: https://youtu.be/TAmYp4jKWoM
Skillshare: https://skl.sh/3nudJ1o
Follow me on twitter for more: https://twitter.com/HunorBorbely
*/
window.addEventListener("DOMContentLoaded", function (event) {
window.focus(); // Capture keys right away (by default focus is on editor)
// Game data
let snakePositions; // An array of snake positions, starting head first
let applePosition; // The position of the apple
let startTimestamp; // The starting timestamp of the animation
let lastTimestamp; // The previous timestamp of the animation
let stepsTaken; // How many steps did the snake take
let score;
let contrast;
let inputs; // A list of directions the snake still has to take in order
let gameStarted = false;
let hardMode = false;
// Configuration
const width = 15; // Grid width
const height = 15; // Grid height
const speed = 200; // Milliseconds it takes for the snake to take a step in the grid
let fadeSpeed = 5000; // milliseconds it takes the grid to disappear (initially)
let fadeExponential = 1.024; // after each score it will gradually take more time for the grid to fade
const contrastIncrease = 0.5; // contrast you gain after each score
const color = "black"; // Primary color
// Setup: Build up the grid
// The grid consists of (width x height) tiles
// The tiles take the the shape of a grid using CSS grid
// The tile can represent a part of the snake or an apple
// Each tile has a content div that takes an absolute position
// The content can fill the tile or slide in or out from any direction to take the shape of a transitioning snake head or tail
const grid = document.querySelector(".grid");
for (let i = 0; i < width * height; i++) {
const content = document.createElement("div");
content.setAttribute("class", "content");
content.setAttribute("id", i); // Just for debugging, not used
const tile = document.createElement("div");
tile.setAttribute("class", "tile");
tile.appendChild(content);
grid.appendChild(tile);
}
const tiles = document.querySelectorAll(".grid .tile .content");
const containerElement = document.querySelector(".container");
const noteElement = document.querySelector("footer");
const contrastElement = document.querySelector(".contrast");
const scoreElement = document.querySelector(".score");
// Initialize layout
resetGame();
// Resets game variables and layouts but does not start the game (game starts on keypress)
function resetGame() {
// Reset positions
snakePositions = [168, 169, 170, 171];
applePosition = 100; // Initially the apple is always at the same position to make sure it's reachable
// Reset game progress
startTimestamp = undefined;
lastTimestamp = undefined;
stepsTaken = -1; // It's -1 because then the snake will start with a step
score = 0;
contrast = 1;
// Reset inputs
inputs = [];
// Reset header
contrastElement.innerText = `${Math.floor(contrast * 100)}%`;
scoreElement.innerText = hardMode ? `H ${score}` : score;
// Reset tiles
for (const tile of tiles) setTile(tile);
// Render apple
setTile(tiles[applePosition], {
"background-color": color,
"border-radius": "50%"
});
// Render snake
// Ignore the last part (the snake just moved out from it)
for (const i of snakePositions.slice(1)) {
const snakePart = tiles[i];
snakePart.style.backgroundColor = color;
// Set up transition directions for head and tail
if (i == snakePositions[snakePositions.length - 1])
snakePart.style.left = 0;
if (i == snakePositions[0]) snakePart.style.right = 0;
}
}
// Handle user inputs (e.g. start the game)
window.addEventListener("keydown", function (event) {
// If not an arrow key or space or H was pressed then return
if (
![
"ArrowLeft",
"ArrowUp",
"ArrowRight",
"ArrowDown",
" ",
"H",
"h",
"E",
"e"
].includes(event.key)
)
return;
// If an arrow key was pressed then first prevent default
event.preventDefault();
// If space was pressed restart the game
if (event.key == " ") {
resetGame();
startGame();
return;
}
// Set Hard mode
if (event.key == "H" || event.key == "h") {
hardMode = true;
fadeSpeed = 4000;
fadeExponential = 1.025;
noteElement.innerHTML = `Hard mode. Press space to start!`;
noteElement.style.opacity = 1;
resetGame();
return;
}
// Set Easy mode
if (event.key == "E" || event.key == "e") {
hardMode = false;
fadeSpeed = 5000;
fadeExponential = 1.024;
noteElement.innerHTML = `Easy mode. Press space to start!`;
noteElement.style.opacity = 1;
resetGame();
return;
}
// If an arrow key was pressed add the direction to the next moves
// Do not allow to add the same direction twice consecutively
// The snake can't do a full turn either
// Also start the game if it hasn't started yet
if (
event.key == "ArrowLeft" &&
inputs[inputs.length - 1] != "left" &&
headDirection() != "right"
) {
inputs.push("left");
if (!gameStarted) startGame();
return;
}
if (
event.key == "ArrowUp" &&
inputs[inputs.length - 1] != "up" &&
headDirection() != "down"
) {
inputs.push("up");
if (!gameStarted) startGame();
return;
}
if (
event.key == "ArrowRight" &&
inputs[inputs.length - 1] != "right" &&
headDirection() != "left"
) {
inputs.push("right");
if (!gameStarted) startGame();
return;
}
if (
event.key == "ArrowDown" &&
inputs[inputs.length - 1] != "down" &&
headDirection() != "up"
) {
inputs.push("down");
if (!gameStarted) startGame();
return;
}
});
// Start the game
function startGame() {
gameStarted = true;
noteElement.style.opacity = 0;
window.requestAnimationFrame(main);
}
// The main game loop
// This function gets invoked approximately 60 times per second to render the game
// It keeps track of the total elapsed time and time elapsed since last call
// Based on that animates the snake either by transitioning it in between tiles or stepping it to the next tile
function main(timestamp) {
try {
if (startTimestamp === undefined) startTimestamp = timestamp;
const totalElapsedTime = timestamp - startTimestamp;
const timeElapsedSinceLastCall = timestamp - lastTimestamp;
const stepsShouldHaveTaken = Math.floor(totalElapsedTime / speed);
const percentageOfStep = (totalElapsedTime % speed) / speed;
// If the snake took a step from a tile to another one
if (stepsTaken != stepsShouldHaveTaken) {
stepAndTransition(percentageOfStep);
// If it’s time to take a step
const headPosition = snakePositions[snakePositions.length - 1];
if (headPosition == applePosition) {
// Increase score
score++;
scoreElement.innerText = hardMode ? `H ${score}` : score;
// Generate another apple
addNewApple();
// Increase the contrast after each score
// Don't let the contrast go above 1
contrast = Math.min(1, contrast + contrastIncrease);
// Debugging
console.log(`Contrast increased by ${contrastIncrease * 100}%`);
console.log(
"New fade speed (from 100% to 0% in milliseconds)",
Math.pow(fadeExponential, score) * fadeSpeed
);
}
stepsTaken++;
} else {
transition(percentageOfStep);
}
if (lastTimestamp) {
// Decrease the contrast based on the time passed an the current score
// With a higher score the contrast decreases slower
const contrastDecrease =
timeElapsedSinceLastCall /
(Math.pow(fadeExponential, score) * fadeSpeed);
// Don't let the contrast drop below zero
contrast = Math.max(0, contrast - contrastDecrease);
}
contrastElement.innerText = `${Math.floor(contrast * 100)}%`;
containerElement.style.opacity = contrast;
window.requestAnimationFrame(main);
} catch (error) {
// Write a note about restarting game and setting difficulty
const pressSpaceToStart = "Press space to reset the game.";
const changeMode = hardMode
? "Back to easy mode? Press the letter E."
: "Ready for hard more? Press the letter H.";
const followMe =
'Follow me <a href="https://twitter.com/HunorBorbely" , target="_top">@HunorBorbely</a>';
noteElement.innerHTML = `${error.message}. ${pressSpaceToStart} <div>${changeMode}</div> ${followMe}`;
noteElement.style.opacity = 1;
containerElement.style.opacity = 1;
}
lastTimestamp = timestamp;
}
// Moves the snake and sets up tiles for the transition function so the transition function will be more effective (the transition function gets called more frequently)
function stepAndTransition(percentageOfStep) {
// Calculate the next position and add it to the snake
const newHeadPosition = getNextPosition();
console.log(`Snake stepping into tile ${newHeadPosition}`);
snakePositions.push(newHeadPosition);
// Start with tail instead of head
// Because the head might step into the previous position of the tail
// Clear tile, yet keep it in the array if the snake grows.
// Whenever the snake steps into a new tile, it will leave the last one.
// Yet the last tile stays in the array if the snake just grows.
// As a sideeffect in case the snake just eats an apple,
// the tail transitioning will happen on a this "hidden" tile
// (so the tail appears as stationary).
const previousTail = tiles[snakePositions[0]];
setTile(previousTail);
if (newHeadPosition != applePosition) {
// Drop the previous tail
snakePositions.shift();
// Set up and start transition for new tail
// Make sure it heads to the right direction and set initial size
const tail = tiles[snakePositions[0]];
const tailDi = tailDirection();
// The tail value is inverse because it slides out not in
const tailValue = `${100 - percentageOfStep * 100}%`;
if (tailDi == "right")
setTile(tail, {
left: 0,
width: tailValue,
"background-color": color
});
if (tailDi == "left")
setTile(tail, {
right: 0,
width: tailValue,
"background-color": color
});
if (tailDi == "down")
setTile(tail, {
top: 0,
height: tailValue,
"background-color": color
});
if (tailDi == "up")
setTile(tail, {
bottom: 0,
height: tailValue,
"background-color": color
});
}
// Set previous head to full size
const previousHead = tiles[snakePositions[snakePositions.length - 2]];
setTile(previousHead, { "background-color": color });
// Set up and start transitioning for new head
// Make sure it heads to the right direction and set initial size
const head = tiles[newHeadPosition];
const headDi = headDirection();
const headValue = `${percentageOfStep * 100}%`;
if (headDi == "right")
setTile(head, {
left: 0, // Slide in from left
width: headValue,
"background-color": color,
"border-radius": 0
});
if (headDi == "left")
setTile(head, {
right: 0, // Slide in from right
width: headValue,
"background-color": color,
"border-radius": 0
});
if (headDi == "down")
setTile(head, {
top: 0, // Slide in from top
height: headValue,
"background-color": color,
"border-radius": 0
});
if (headDi == "up")
setTile(head, {
bottom: 0, // Slide in from bottom
height: headValue,
"background-color": color,
"border-radius": 0
});
}
// Transition head and tail between two steps
// Called with every animation frame, except when stepping to a new tile
function transition(percentageOfStep) {
// Transition head
const head = tiles[snakePositions[snakePositions.length - 1]];
const headDi = headDirection();
const headValue = `${percentageOfStep * 100}%`;
if (headDi == "right" || headDi == "left") head.style.width = headValue;
if (headDi == "down" || headDi == "up") head.style.height = headValue;
// Transition tail
const tail = tiles[snakePositions[0]];
const tailDi = tailDirection();
const tailValue = `${100 - percentageOfStep * 100}%`;
if (tailDi == "right" || tailDi == "left") tail.style.width = tailValue;
if (tailDi == "down" || tailDi == "up") tail.style.height = tailValue;
}
// Calculate to which tile will the snake step into
// Throw error if the snake bites its tail or hits the wall
function getNextPosition() {
const headPosition = snakePositions[snakePositions.length - 1];
const snakeDirection = inputs.shift() || headDirection();
switch (snakeDirection) {
case "right": {
const nextPosition = headPosition + 1;
if (nextPosition % width == 0) throw Error("The snake hit the wall");
// Ignore the last snake part, it'll move out as the head moves in
if (snakePositions.slice(1).includes(nextPosition))
throw Error("The snake bit itself");
return nextPosition;
}
case "left": {
const nextPosition = headPosition - 1;
if (nextPosition % width == width - 1 || nextPosition < 0)
throw Error("The snake hit the wall");
// Ignore the last snake part, it'll move out as the head moves in
if (snakePositions.slice(1).includes(nextPosition))
throw Error("The snake bit itself");
return nextPosition;
}
case "down": {
const nextPosition = headPosition + width;
if (nextPosition > width * height - 1)
throw Error("The snake hit the wall");
// Ignore the last snake part, it'll move out as the head moves in
if (snakePositions.slice(1).includes(nextPosition))
throw Error("The snake bit itself");
return nextPosition;
}
case "up": {
const nextPosition = headPosition - width;
if (nextPosition < 0) throw Error("The snake hit the wall");
// Ignore the last snake part, it'll move out as the head moves in
if (snakePositions.slice(1).includes(nextPosition))
throw Error("The snake bit itself");
return nextPosition;
}
}
}
// Calculate in which direction the snake's head is moving
function headDirection() {
const head = snakePositions[snakePositions.length - 1];
const neck = snakePositions[snakePositions.length - 2];
return getDirection(head, neck);
}
// Calculate in which direction of the snake's tail
function tailDirection() {
const tail1 = snakePositions[0];
const tail2 = snakePositions[1];
return getDirection(tail1, tail2);
}
function getDirection(first, second) {
if (first - 1 == second) return "right";
if (first + 1 == second) return "left";
if (first - width == second) return "down";
if (first + width == second) return "up";
throw Error("the two tile are not connected");
}
// Generates a new apple on the field
function addNewApple() {
// Find a position for the new apple that is not yet taken by the snake
let newPosition;
do {
newPosition = Math.floor(Math.random() * width * height);
} while (snakePositions.includes(newPosition));
// Set new apple
setTile(tiles[newPosition], {
"background-color": color,
"border-radius": "50%"
});
// Note that the apple is here
applePosition = newPosition;
}
// Resets size and position related CSS properties
function setTile(element, overrides = {}) {
const defaults = {
width: "100%",
height: "100%",
top: "auto",
right: "auto",
bottom: "auto",
left: "auto",
"background-color": "transparent"
};
const cssProperties = { ...defaults, ...overrides };
element.style.cssText = Object.entries(cssProperties)
.map(([key, value]) => `${key}: ${value};`)
.join(" ");
}
});
Also see: Tab Triggers