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HTML

              
                <canvas id = "gameCanvas" width = "800" height = "600"></canvas>
              
            
!

CSS

              
                
              
            
!

JS

              
                var canvas;
var canvasContext;
var ballX = 50;
var ballY = 50;
var ballSpeedX = 10;
var ballSpeedY = 4;
    
var player1Score = 0;
var player2Score = 0;
const WINNING_SCORE = 5;

var showWinScreen = false;
    
var paddle1Y = 250;
var paddle2Y = 250;
const PADDLE_THICKNESS = 10;
const PADDLE_HEIGHT = 100;
    
function calculateMousePos( evt ) {
    var rect = canvas.getBoundingClientRect();
    var root = document.documentElement;
    var mouseX = evt.clientX - rect.left - root.scrollLeft;
    var mouseY = evt.clientY - rect.top - root.scrollTop;
    return {
        x:mouseX,
        y:mouseY
    };
}
    
function handleMouseClick ( evt ) {
    if( showWinScreen ) {
        player1Score = 0;
        player2Score = 0;
        showWinScreen = false;
    }
}    

window.onload = function() {
    canvas = document.getElementById( 'gameCanvas' );
    canvasContext = canvas.getContext( '2d' );
    
    var framesPerSecond = 30;
    setInterval( function () {
        moveEverything();
        drawEverything();
    }, 1000/framesPerSecond );
    
    canvas.addEventListener( 'mousedown', handleMouseClick);
    
    canvas.addEventListener( 'mousemove', 
            function ( evt ) {
                    var mousePos = calculateMousePos( evt );
                    paddle1Y = mousePos.y - ( PADDLE_HEIGHT / 2 );
    } );
}

function ballReset() {
    if( player1Score >= WINNING_SCORE || player2Score >= WINNING_SCORE ) {
        showWinScreen = true;
    }
    ballSpeedX = -ballSpeedX;
    ballX = canvas.width / 2;
    ballY = canvas.height / 2;
}
    
function computerMovement() {
    var paddle2YCenter = paddle2Y + ( PADDLE_HEIGHT / 2 );
    if( paddle2YCenter < ballY - 35 ) {
        paddle2Y += 6;
    }
    else if( paddle2YCenter > ballY + 35 ) {
        paddle2Y -= 6;
    }
}

function moveEverything() {
    if( showWinScreen ) {
        return;
    }
    computerMovement();
    
    ballX += ballSpeedX;
    ballY += ballSpeedY;
    if( ballX < 0 ) {
        if( ballY > paddle1Y && ballY < paddle1Y + PADDLE_HEIGHT ){
            ballSpeedX = -ballSpeedX;
            var deltaY = ballY -( paddle1Y + PADDLE_HEIGHT / 2 );
            ballSpeedY = deltaY * 0.35;
        }
        else {
            player2Score++; //must be BEFORE ball reset
            ballReset();
        }
    }
    if( ballX > canvas.width ){
        if( ballY > paddle2Y && ballY < paddle2Y + PADDLE_HEIGHT ){
            ballSpeedX = -ballSpeedX;
            var deltaY = ballY -( paddle2Y + PADDLE_HEIGHT / 2 );
            ballSpeedY = deltaY * 0.35;
        }
        else {
            player1Score++; //must be BEFORE ball reset
            ballReset();
        }
    }
    if( ballY < 0 ) {
        ballSpeedY = -ballSpeedY;
    }
    if( ballY > canvas.height ) {
        ballSpeedY = -ballSpeedY;
    }
}

function drawNet() {
    for( var i = 0; i < canvas.height; i += 40 ) {
        colorRect( canvas.width / 2 - 1, i, 2, 20, 'white' );
    }
}
    
function drawEverything() {
    //blanks out screen with black
    colorRect( 0, 0, canvas.width, canvas.height, 'black' );
    
    if( showWinScreen ) {
        canvasContext.fillStyle = 'white';
        canvasContext.font = "20px sans-serif";
        
        if( player1Score >= WINNING_SCORE ) {
            canvasContext.fillText( "Left Player Won!", 330, 200 );
        } 
        else if( player2Score >= WINNING_SCORE ) {
            canvasContext.fillText( "Right Player Won!", 330, 200 );
            
        }
            
        canvasContext.font = "15px sans-serif";
        canvasContext.fillText( "Click to Continue", 350, 350 );
        return;
    }
    
    drawNet();
    
    //left player paddle
    colorRect( 0, paddle1Y, PADDLE_THICKNESS, PADDLE_HEIGHT, 'white' );
    //right player paddle
    colorRect( canvas.width - PADDLE_THICKNESS, paddle2Y, 10, PADDLE_HEIGHT, 'white' );
    //ball
    colorCircle( ballX, ballY, 7, 'white' );
    //score
    canvasContext.fillText( player1Score, 100, 100 );
    canvasContext.fillText( player2Score, canvas.width - 100, 100 );
}
    
function colorCircle( centerX, centerY, radius, drawColor ) {
    canvasContext.fillStyle = drawColor;
    canvasContext.beginPath();
    canvasContext.arc( centerX, centerY, radius, 0, Math.PI * 2, true);
    canvasContext.fill();
}    

function colorRect( leftX, topY, width, height, drawColor ) {
    canvasContext.fillStyle = drawColor;
    canvasContext.fillRect( leftX, topY, width, height );
}
              
            
!
999px

Console