先写一个敌机类

/*创建敌机： */function Enemy(blood,speed,imgs){    //敌机left    this.left = 0;    //敌机top    this.top = 0;    //敌机血量    this.blood = blood;    //敌机速度    this.speed = speed;    //敌机图片集合    this.imgs = imgs;//爆炸前和爆炸后}Enemy.prototype = {    constructor:Enemy,    init:function(){        //创建一个元素        var img = document.createElement('img');        //将图片路径赋值给它        img.src=this.imgs[0];        //插入到game中        Engine.game.appendChild(img);        //赋值给敌机的初始图片        this.self = img;        //当图片加载完成以后获取图片的高度和宽度        var _this = this;//在函数里面this的指向会改变，所以我们提前报存下来        img.onload = function(){                        _this.left = parseInt(Math.random()*(320-img.offsetWidth));            _this.top = -img.offsetHeight;            img.style.left = _this.left+'px';            img.style.top = _this.top+'px';        };        //生成敌机编号并放入引擎的bullet中        this.id = Math.random();        Engine.enemy[this.id]=this;    },    //子弹移动，定时器都交给引擎去做    move:function(){        this.top+=this.speed;        this.self.style.top = this.top+'px';        //越界判断        if(this.top>568+this.self.offsetWidth){            this.destroy();        }    },    destroy:function(){        //销毁        //从页面小时        this.self.remove();        //从内存消失        delete Engine.bullet[this.id];    }}

在去创建小型 中型 大型敌机

/*创建所有类型的飞机 */function SmallEnemy(){    var s = parseInt(Math.random()*3+3);    Enemy.call(this,1,s,['image/enemy1.png','image/enemy1-bang.gif'])}SmallEnemy.prototype = {    constructor:SmallEnemy;    __proto__:Enemy.prototype;}function MiddleEnemy(){    var s = parseInt(Math.random()*3+2);    Enemy.call(this,5,s,['image/enemy2.png','image/enemy2-bang.gif'])}MiddleEnemy.prototype = {    constructor:MiddleEnemy;    __proto__:Enemy.prototype;}function LargeEnemy(){    var s = parseInt(Math.random()*2+1);    Enemy.call(this,10,s,['image/enemy3.png','image/enemy3-bang.gif'])}LargeEnemy.prototype = {    constructor:LargeEnemy;    __proto__:Enemy.prototype;}

去引擎里面不间断的创建敌机

/*游戏引擎 */var Engine = {    //刚开始的游戏状态    gameStatus:false,    //所以敌机    enemy:{},    //子弹    bullet:{},    //得分    score:0,    //背景图片    game:document.querySelector('.game'),    //初始化    init:function(){        this.gameStart();    },    //游戏开始    gameStart:function(){        var _this = this;        //点击图片的时候判断游戏状态        this.game.onclick = function(){            if(!_this.gameStatus){                _this.gameStatus = true;                //移动移动                _this.bgMove();                _this.handleMove();                _this.createPlane();            }        }    },    //背景移动    bgMove:function(){        var y=0;        var _this = this;        this.bgTimer = setInterval(function(){            y+=2;            _this.game.style['background-position-y']=y+'px';        },50)    },    createPlane:function(){        //创建敌机和英雄机        Hero.init();        //创建敌机        var timer = setInterval(function(){            var num = parseInt(Math.random()*15)+1;            switch (num) {                case 1:                case 3:                case 5:                case 7:                case 9:                    new SmallEnemy().init();                    break;                case 2:                case 4:                case 6:                    new MiddleEnemy().init();                case 8:                case 12:                    new LargeEnemy().init();                                                }        },500)    },    //所有敌机和子弹都要动    handleMove:function(){        var _this=this;        var timer = setInterval(function(){            //创建所有子弹            for(var i in _this.bullet){                _this.bullet[i].move()            }            //c创建所有敌机动            for(var i in _this.enemy){                _this.enemy[i].move()            }        },30)    }};Engine.init();