javascript的继承，一个简单的乒乓球游戏

$(document).ready(function() {        //球的类var Ball = function(x, y) {this.X = x;this.Y = y;this.style = {width : "5px",height : "5px",color : "#E00"};this.direction = "downright";this.time;};Ball.prototype = function() {var initBall = function() {var balldiv = document.createElement('div');$(balldiv).css({"position" : "absolute","left" : this.X + "px","top" : this.Y + "px","width" : this.style.width,"height" : this.style.height,"background-color" : this.style.color});balldiv = bindMove.call(this, balldiv);$('body').append(balldiv);};var bindMove = function(div) {this.time = setInterval($.proxy(function(){moveBall.call(this, div);//changeDirection.call(this, div);}, this), 100);return div;};var changeDirection = function(div) {if(this.X < 10) { //撞到左边墙if("upleft" == this.direction){this.direction = "upright";moveBall.call(this, div);}else if("downleft" == this.direction){this.direction = "downright";moveBall.call(this, div);}}else if(this.X > 803) { //撞到右边墙if("upright" == this.direction){this.direction = "upleft";moveBall.call(this, div);}else if("downright" == this.direction){this.direction = "downleft";moveBall.call(this, div);}}if(this.Y < 10) { //撞到顶部gameOver.call(this);}else if(this.Y > 403) { //掉到底部gameOver.call(this);}var bBatPos = blackBat.getBatPosition();if(bBatPos.X_head < this.X && bBatPos.X_tail > this.X && bBatPos.Y - 5 <= this.Y) { //撞到黑拍子上if("downright" == this.direction){this.direction = "upright";moveBall.call(this, div);}else if("downleft" == this.direction) {this.direction = "upleft";moveBall.call(this, div);}}var gBatPos = greenBat.getBatPosition();if(gBatPos.X_head < this.X && gBatPos.X_tail > this.X && gBatPos.Y + 5 >= this.Y) { //撞到绿拍子上if("upright" == this.direction){this.direction = "downright";moveBall.call(this, div);}else if("upleft" == this.direction) {this.direction = "downleft";moveBall.call(this, div);}}};var moveBall = function(div) {switch(this.direction){case "upright" : moveUpRight.call(this, div);break;case "upleft" : moveUpLeft.call(this, div);break;case "downright" :moveDownRight.call(this, div);break;case "downleft" : moveDownLeft.call(this, div);break;}changeDirection.call(this, div);}var moveUpLeft = function(div) {this.X = this.X - 3;this.Y = this.Y - 3;$(div).css({"left" : this.X,"top" : this.Y});};var moveUpRight = function(div) {this.X = this.X + 3;this.Y = this.Y - 3;$(div).css({"left" : this.X,"top" : this.Y});};var moveDownLeft = function(div) {this.X = this.X - 3;this.Y = this.Y + 3;$(div).css({"left" : this.X,"top" : this.Y});};var moveDownRight = function(div) {this.X = this.X + 3;this.Y = this.Y + 3;$(div).css({"left" : this.X,"top" : this.Y});};var gameOver = function() {alert("GAME OVER!");clearInterval(this.time);};return {initBall : initBall};}();var Bat = function() {};//球拍的类，用作父类Bat.prototype = function() {var initBat = function() {var batdiv = document.createElement('div');$(batdiv).css({"position" : "absolute","left" : this.X + "px","top" : this.Y + "px","width" : this.style.width,"height" : this.style.height,"background-color" : this.style.color});batdiv = bindMove.call(this, batdiv);$('body').append(batdiv);};var bindMove = function(div) {$('body').keydown($.proxy(function(e) {//得到键盘对应的字母var realkey = String.fromCharCode(e.which);switch(realkey) {case this.control.toleft : moveLeft.call(this, div);break;case this.control.toright :moveRight.call(this, div);break;};}, this));return div;};var moveLeft = function(div) {if(this.X > 10) {this.X = this.X - 3;$(div).css("left", this.X + "px");}};var moveRight = function(div) {if(this.X < 728) {this.X = this.X + 3;$(div).css("left", this.X + "px");}};var getBatPosition = function() {return {X_head : this.X,X_tail : this.X + 80,Y : this.Y};};return {initBat : initBat,getBatPosition : getBatPosition};}();var BlackBat = function(x) {this.X = x;this.Y = 400;this.style = {width : "80px",height : "5px",color : "#000"};this.control = {toleft : 'A',toright : 'D'};}//继承父类BatBlackBat.prototype = new Bat();var GreenBat = function(x) {this.X = x;this.Y = 10;this.style = {width : "80px",height : "5px",color : "#0EE"};this.control = {toleft : 'J',toright : 'L'};}GreenBat.prototype = new Bat();//实现var blackBat = new BlackBat(300);blackBat.initBat();var greenBat = new GreenBat(300);greenBat.initBat();var ball = new Ball(50, 50);ball.initBall();    });