pong.js Example File
script/context2d/scripts/pong.js

 // globals
 playarea_canvas = document.getElementById('tutorial');
 playarea_canvas.resize(320,200);
 playarea = playarea_canvas.getContext('2d');
 //p1_scr = document.getElementById('p1_scr');
 //p2_scr = document.getElementById('p2_scr');
 //status_msg = document.getElementById('status');
 //debug = document.getElementById('debug');
 ball_direction = 0;
 up = -1;
 down = 1;

 //key codes
 key_up = 38;
 key_down = 40;
 key_W = 87;
 key_S = 83;
 key_pause = 32;

 speed = 2;                      //controls the speed of the ball
 paddle_inc = 10;        //how many pixels paddle can move in either direction
 pause = false;

 player_1 = 0;           //player IDs
 player_2 = 1;
 player_1_scr = 0;       //player scores
 player_2_scr = 0;
 player_1_direction = null;      //null = no movement whatsoever
 player_2_direction = null;

 pa = new Array();
 divider = new Array();
 paddle_1 = new Array();
 paddle_2 = new Array();
 ball = new Array();

 function sleep(numberMillis)
 {
     var now = new Date();
     var exitTime = now.getTime() + numberMillis;
     while (true) {
         now = new Date();
         if (now.getTime() > exitTime)
             return;
     }
 }

 function init()
 {
     pa['width'] = 150;
     pa['height'] = 140;
     pa['player_margin'] = 10;           //area behind player paddles
     pa['foreground'] = "#FFFFFF";
     pa['background'] = "#000000";

     divider['pos'] = pa['width']/2;
     divider['width'] = 4;

     paddle_1['width'] = 8;
     paddle_1['height'] = 64;
     paddle_1['x'] = pa['player_margin'];
     paddle_1['y'] = (pa['height'] /2 ) - (paddle_1['height'] / 2);

     paddle_2['width'] = 8;
     paddle_2['height'] = 64;
     paddle_2['x'] = (pa['width'] - pa['player_margin'] - paddle_2['width']);
     paddle_2['y'] = (pa['height'] /2 ) - (paddle_2['height'] / 2);

     ball['width'] = 10;
     ball['height'] = 10;
     ball['x'] = (pa['width']/2) - (ball['width'] / 2);
     ball['y'] = (pa['height']/2) - (ball['height'] / 2);

     ball_direction = Math.random() * 360;       //initialize ball direction, which is determined by angle, at random
     speed = 2;
 }

 function renderPlayarea()
 {
     playarea.beginPath();

     playarea.clearRect(0,0,pa['width'],pa['height']);
     playarea.fillStyle = pa['background'];
     playarea.strokeStyle = pa['foreground'];
     playarea.fillRect(0,0, pa['width'], pa['height']);

     //move paddles
     if(player_1_direction != null)
         {
             if(player_1_direction == up)
                 paddle_1['y'] = paddle_1['y'] - paddle_inc;
             else
                 paddle_1['y'] = paddle_1['y'] + paddle_inc;
         }
     if(player_2_direction != null)
         {
             if(player_2_direction == up)
                 paddle_2['y'] = paddle_2['y'] - paddle_inc;
             else
                 paddle_2['y'] = paddle_2['y'] + paddle_inc;
         }
     playarea.rect(paddle_1['x'],paddle_1['y'],paddle_1['width'],paddle_1['height']);
     playarea.rect(paddle_2['x'],paddle_2['y'],paddle_2['width'],paddle_2['height']);

     //move ball
     playarea.rect(ball['x'], ball['y'], ball['width'], ball['height']);
     ball['x'] = ball['x'] + Math.cos((ball_direction)*Math.PI/180) * speed;
     ball['y'] = ball['y'] + Math.sin((ball_direction)*Math.PI/180) * speed;

     playarea.fillStyle = pa['foreground'];
     playarea.fill();

     playarea.beginPath();
     //redraw divider
     playarea.lineWidth = divider['width'];
     playarea.lineTo(divider['pos'], 0);
     playarea.lineTo(divider['pos'], pa['height'] = 200);
     playarea.lineWidth = 1;

     playarea.stroke();
     playarea.closePath();
 }

 function testCollisions()
 {
     //make sure paddles don't go beyond play area
     if(((paddle_1['y'] <= 0) && (player_1_direction == up)) || ((paddle_1['y'] >= (pa['height'] - paddle_1['height'])) && (player_1_direction == down)))
         player_1_direction = null;
     if(((paddle_2['y'] <= 0) && (player_2_direction == up)) || ((paddle_2['y'] >= (pa['height'] - paddle_2['height'])) && (player_2_direction == down)))
         player_2_direction = null;

     //check to see if ball went beyond paddles, and if so, score accordingly and reset playarea
     if(ball['x'] <= 0)
         {
             setScore(player_2);
             init()
                 sleep(1000);
         }
     if(ball['x'] >= (pa['width'] - ball['width']))
         {
             setScore(player_1);
             init();
             sleep(1000);
         }

     //check to see if ball hit top or bottom wall. if so, change direction
     if((ball['y'] >= (pa['height'] - ball['height'])) || ball['y'] <= 0)
         ball_direction = -ball_direction;

     //check to see if the ball hit a paddle, and if so, change ball angle dependant on where it hit the paddle
     if((ball['x'] <= (paddle_1['x'] + paddle_1['width'])) && (ball['y'] >= paddle_1['y']) && (ball['y'] <= (paddle_1['y'] + paddle_1['height'])))
         {
             ball_direction = -ball_direction/2;
             speed += .5;
         }
     if(((ball['x'] + ball['width']) >= paddle_2['x']) && (ball['y'] >= paddle_2['y']) && (ball['y'] <= (paddle_2['y'] + paddle_2['height'])))
         {
             ball_direction = (180+ball_direction)/2;
             speed += .5;
         }
 }

 function setScore(p)
 {
     if(p == player_1)
         {
             player_1_scr++;
             //p1_scr.firstChild.nodeValue = player_1_scr;
         }
     if(p == player_2)
         {
             player_2_scr++;
             //p2_scr.firstChild.nodeValue = player_2_scr;
         }
 }

 //handle input
 document.onkeydown = function(ev)
 {
     switch(ev.keyCode)
     {
         case key_W:
         player_1_direction = up;
         break;
         case key_S:
         player_1_direction = down;
         break;
         case key_up:
         player_2_direction = up;
         break;
         case key_down:
         player_2_direction = down;
         break;
     }
 }

 document.onkeyup = function(ev)
 {
     switch(ev.keyCode)
     {
         case key_W:
         case key_S:
         player_1_direction = null;
         break;
         case key_up:
         case key_down:
         player_2_direction = null;
         break;
         case key_pause:
         if(pause == false)
         {
             clearInterval(game);
             //status_msg.style.visibility = "visible";
             pause = true;
         }
         else
         {
             game = setInterval(main, 25);
             //status_msg.style.visibility = "hidden";
             pause = false;
         }
         break;
     }
 }

 function main()
 {
     testCollisions();
     renderPlayarea();
 }

 init();
 game = setInterval(main, 25);