Creating a Car Game in React - Part 4 - Score

June 24, 2019

This is the fourth part of a series (that began here). So far, we have a game where you can whizz around the screen avoiding trees. This effectively encompasses most aspects of a game of this type; that is, you can move, and there is a something preventing you.

The next step is to introduce something for the player to try to do, and give a score based on that. In our case, our player is going to try and collect cups - as per the original game. The asset I’ve created for the cup is here. For anyone following this series, you may have noticed that my artwork is a little… crap.

The source for this post is here.


The first thing that we’ve done here is added some code to place a few cups around the screen; the code for this was essentially the same as build obstacles:

placeCups() {
	let cups = [];
	const cupCount = 1;
	for (let i = 1; i <= cupCount; i++) {
		const centreX = Math.floor(Math.random() \* this.state.windowWidth) + 1;
		const centreY = Math.floor(Math.random() \* this.state.windowHeight) + 1; 
		cups.push(<GameItem key={i} image={cupImg} centreX={centreX} centreY={centreY} width={this.spriteWidth} height={this.spriteHeight} itemType={2} />);
	return cups;

In a later post, I hope to do a full refactor, but for now, we have a separate function. This is rendered in the same way as the obstacles:

render() { 
	return <div onKeyDown={this.onKeyDown} tabIndex="0">
		<GameStatus Lives={this.state.playerLives} Message={this.state.message} Score={this.state.score} />
		<Background backgroundImage={backgroundImg}
		windowWidth={this.state.windowWidth} windowHeight={this.state.windowHeight} /> 
		<Car carImage={this.state.playerCrashed ? brokenCarImg : carImg} 
		centreX={this.state.playerX} centreY={this.state.playerY} 
		width={this.spriteWidth} height={this.spriteHeight} 
		rotation={this.state.playerRotation} /> 

Collecting cups

In order to collect something, the player must collide with it. We need to change the collision code slightly to make it a little more re-usable:

detectAnyCollision(rect1) { 
	// Have we crashed or left the screen
	if (this.detectOutScreen(rect1)) {
		return true;
	let collided = this.detectGameItemCollision(this.halfWidth, this.halfHeight, rect1, this.obstacles);
	if (collided !== undefined) {
		return true;
	return false;

detectGameItemCollision(halfWidth, halfHeight, rect1, gameItemList) {
	const collided = gameItemList.find(a => {
		var rect2 = {
			x: a.props.centreX - halfWidth, y: a.props.centreY - halfHeight,
			width: this.spriteWidth, height: this.spriteHeight
		return (this.detectCollision(rect1, rect2));
	return collided;

As you can see, we now have a function that returns the item that we collided with, rather than a simple boolean. We then use this at the end of the game loop to determine whether we collided with a cup:

// Check for collected cup
const item = this.detectGameItemCollision(this.halfWidth, this.halfHeight, rect1, this.cups);
if (item !== undefined) {


There’s little point in zooming around collecting cups, if there’s no permanent record, so we need to add a score. Let’s start with a state variable in game.jsx:

this.state = {
	playerX: 100,
	playerY: 100,
	windowWidth: 1500,
	windowHeight: 1500,
	playerMomentum: 0,
	playerRotation: 0,
	playerVelocityX: 0,
	playerVelocityY: 0,
	playerLives: 3,
	playerCrashed: false,
	gameLoopActive: false,
	message: "",
	score: 0

And here’s the collectedCup function we mentioned a second ago:

collectedCup(key) {
	this.setState({ score: this.state.score + 1 });
	this.cups = this.cups.filter(cup => cup.key != key);
	this.updateMessage("Collected cup");

All we’re doing here is simply updating the score and then removing that cup from the list.

The final part is to display the score on the screen; let’s have a look at our updated GameStatus.jsx:

function GameStatus(props) {
	const flexStyle = {
		display: 'flex',
		position: 'absolute',
		zIndex: 1,
		margin: 20,
		justifyContent: 'center',
		alignItems: 'center',
		width: '100%'
	const labelStyle = { 
		zIndex: 1,
		margin: 50
	return ( 
		<div className="flex-container" style={flexStyle}>
			<label style={labelStyle}>
				Lives Remaining: {props.Lives}
			<label style={labelStyle}>
				Score: {props.Score}
			<label style={labelStyle}>

As you can see, we’re just displaying the score as part of the status.

In the next post, we’ll have a look at the concept of levels, and introduce a time limit.


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