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JavaScript打造的小游戏贪吃蛇(详解)

作者:CNwander
测试:IE7 FF3.0.14


提示:可修改后代码再运行!

Tips: (老鸟跳过,希望对新手有所帮助)

IE: element.innerText = FF: element.textContent;
setAttribute("cellpadding","0")在IE中无效,正确写法cellPadding (一不小心就犯错了);
FF中,使用绑定在某元素上的键盘事件前,先让它获得焦点,document也不例外,这容易疏忽;
在IE中create table element,记得加tbody;
代码(有详细注释):

以下为引用的内容:
// code by CNwander.
// common
function $(str) {
    return document.getElementById(str);
}
function $tag(str,target) {
    target = target || document;
    return target.getElementsByTagName(str);
}
// global
// const
var WIDTH = 20, //网格宽度
    HEIGHT = 20, //网格高度
    SAY = ["相当不错,虽然说和CNwander还不是一个级别的","可以啊,再加点油都可以和CNwander媲美了!","一个字,牛,连CNwander都甘拜下风了","差不多行了,别把游戏玩爆了"];
var len = 3, //蛇的长度
    speed, //爬行速度
    gridElems = multiArray(WIDTH,HEIGHT), //单元格对象
    carrier, //承载对象(食物,障碍,滑板,刹车)
    snake, //蛇每节的坐标点
    info, //交互对话
    btnStart, //开始按钮
    topScore = len,
    snakeTimer, //蛇行走计时器
    brakeTimers = [], //随机刹车
    skateTimers = [], //随机滑板
    directkey; // 方向键值 37-40 左上右下
window.onload = function(){
    info = $("say");
    btnStart = $("btnStart");
    initGrid(); //网格初始化
    document.onkeydown = attachEvents; //绑定方向事件
    btnStart.onclick = function (e) {
        btnStart.blur(); //firefox中必须释放焦点
        start(); //游戏开始
        btnStart.setAttribute("disabled",true);
        btnStart.style.color = "#aaa";
    }
}
//开始游戏
function start() {
    len = 3;
    speed = 10;
    directkey = 39;
    carrier = multiArray(WIDTH,HEIGHT);
    snake = new Array();
    clear();
    initSnake(); //蛇初始化
    addObject("food");
    walk();
    addRandomBrake();
}
//创建网格
function initGrid() {
    var body = $tag("body")[0];
    var table = document.createElement("table"),
        tbody = document.createElement("tbody")
    for(var j = 0; j < HEIGHT; j++) { 
        var col = document.createElement("tr"); 
        for(var i = 0; i < WIDTH; i++) { 
            var row = document.createElement("td");
            gridElems[i][j] = col.appendChild(row); 
        }
        tbody.appendChild(col); 
    }
    table.appendChild(tbody);
    $("snakeWrap").appendChild(table);
}
//创建蛇
function initSnake() {
    var pointer = randomPointer(len-1, len-1, WIDTH/2);
    for(var i = 0; i < len; i++) {
        var x = pointer[0] - i,
            y = pointer[1];
        snake.push([x,y]);
        carrier[x][y] = "cover";
    }
}
//添加键盘事件
function attachEvents(e) {
    e = e || event;
    directkey = Math.abs(e.keyCode - directkey) != 2 && e.keyCode > 36 && e.keyCode < 41 ? e.keyCode : directkey; //非方向键、反向无效
    return false;
}
function walk() {
    if(snakeTimer) window.clearInterval(snakeTimer);
    snakeTimer = window.setInterval(step, Math.floor(3000/speed));
}
function step() {
    //获取目标点
    var headX = snake[0][0],
        headY = snake[0][1];
    switch(directkey) {
        case 37: headX -= 1; break;
        case 38: headY -= 1; break;
        case 39: headX += 1; break
        case 40: headY += 1; break;
    }
    //碰到边界,阻挡物,则结束游戏
    if(headX >= WIDTH || headX < 0 || headY >= HEIGHT || headY < 0 || carrier[headX][headY] == "block" || carrier[headX][headY] == "cover" ) {
        trace("GAME OVER");
        if(getText($("score"))*1 < len) trace(len,$("score"));
        btnStart.removeAttribute("disabled");
        btnStart.style.color = "#000";
        window.clearInterval(snakeTimer);
        for(var i = 0; i < brakeTimers.length; i++) window.clearTimeout(brakeTimers[i]);
        for(var i = 0; i < skateTimers.length; i++) window.clearTimeout(skateTimers[i]);
        return;
    }
    //加速
    if(len % 4 == 0 && speed < 60 && carrier[headX][headY] == "food") {
        speed += 5;
        walk();   
        trace("加速!");
    }
    //捡到刹车
    if(carrier[headX][headY] == "brake") {
        speed = 5;
        walk();
        trace("恭喜!捡到刹车一个。");
    }
    //遭遇滑板
    if(carrier[headX][headY] == "skate") {
        speed += 20;
        walk();
        trace("遭遇滑板!");
    }   
    //添加阻挡物
    if(len % 6 == 0 && len < 60 && carrier[headX][headY] == "food") {
        addObject("block");
    }   
    //对话
    if(len <= 40 && len % 10 == 0) {
        var cheer = SAY[len/10-1];
        trace(cheer);
    }   
    //吃东西
    if(carrier[headX][headY] != "food") {
        var lastX = snake[snake.length-1][0],
            lastY = snake[snake.length-1][1];
        carrier[lastX][lastY] = false;
        gridElems[lastX][lastY].className = "";
        snake.pop();
    } else {
        carrier[headX][headY] = false;
        trace("吃到食物");
        addObject("food");
    }
    snake.unshift([headX,headY]);
    carrier[headX][headY] = "cover";
    gridElems[headX][headY].className = "cover";
   
    len = snake.length;
}
//添加物品
function addObject(name) {
    var p = randomPointer();
    carrier[p[0]][p[1]] = name;
    gridElems[p[0]][p[1]].className = name;
}
//添加随机数量刹车和滑板
function addRandomBrake() {
    var num = randowNum(1,5);
    for(var i = 0; i < num; i++) {
        brakeTimers.push( window.setTimeout(function(){addObject("brake")},randowNum(10000,100000)) );
        skateTimers.push( window.setTimeout(function(){addObject("skate")},randowNum(5000,100000)) );
    }        
}
//输出信息
function trace(sth,who) {
    who = who || info;
    if(document.all) who.innerText = sth;
    else who.textContent = sth;
}
//获取信息
function getText(target) {
    if(document.all) return target.innerText;
    else return target.textContent;
}
//创建二维数组
function multiArray(m,n) {
    var arr =  new Array(n);
    for(var i=0; i<m; i++)
        arr[i] = new Array(m);
    return arr;
}
//清除画面
function clear() {
    for(var y = 0; y < gridElems.length; y++) {
        for(var x = 0; x < gridElems[y].length; x++) {
            gridElems[x][y].className = "";
        }
    }
}
//产生指定范围随机点 烈火网www.veryhuo.com
function randomPointer(startX,startY,endX,endY) {
    startX = startX || 0;
    startY = startY || 0;
    endX = endX || WIDTH;
    endY = endY || HEIGHT;
    var p = [],
        x = Math.floor(Math.random()*(endX - startX)) + startX,
        y = Math.floor(Math.random()*(endY - startY)) + startY;
    if(carrier[x][y]) return randomPointer(startX,startY,endX,endY);
    p[0] = x;
    p[1] = y;
    return p;
}
//产生随机整数
function randowNum(start,end) {
    return Math.floor(Math.random()*(end - start)) + start;
}

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