canvas学习笔记04

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几天没写了，由于javascript是半桶水，导致canvas总是走走停停。

今天用到了设计模式，中介者模式。

由于js中的继承很~~。好变态的面向对象~~ 下面是大牛写的js的继承框架。

(function(){  var initializing = false, fnTest = /xyz/.test(function(){xyz;}) ? /\b_super\b/ : /.*/;   // The base Class implementation (does nothing)  this.Class = function(){};   // Create a new Class that inherits from this class  Class.extend = function(prop) {    var _super = this.prototype;       // Instantiate a base class (but only create the instance,    // don't run the init constructor)    initializing = true;    var prototype = new this();    initializing = false;       // Copy the properties over onto the new prototype    for (var name in prop) {      // Check if we're overwriting an existing function      prototype[name] = typeof prop[name] == "function" &&        typeof _super[name] == "function" && fnTest.test(prop[name]) ?        (function(name, fn){          return function() {            var tmp = this._super;                       // Add a new ._super() method that is the same method            // but on the super-class            this._super = _super[name];                       // The method only need to be bound temporarily, so we            // remove it when we're done executing            var ret = fn.apply(this, arguments);                    this._super = tmp;                       return ret;          };        })(name, prop[name]) :        prop[name];    }       // The dummy class constructor    function Class() {      // All construction is actually done in the init method      if ( !initializing && this.init )        this.init.apply(this, arguments);    }       // Populate our constructed prototype object    Class.prototype = prototype;       // Enforce the constructor to be what we expect    Class.prototype.constructor = Class;     // And make this class extendable    Class.extend = arguments.callee;       return Class;  };})();

使用方法是：

先创建一个类：

var my_class = Class.extend({       //构造函数init:function(a){           this.a = a;        }});

创建一个对象 my_object = new myclass("duixiang");

另外：js中的回调函数如的形式如果是这样：

xxx("xx",callback());

那么callback()中的this是window对象。

还有一类：

xx.onxxxx = function(){}

function中的this是xx

关于闭包传参的经典问题是：

for(var i =0;i<5;i++){  setTimeout(function(){console.log(i);},1000*i);}

打印输出是5个5；程序应该解读为，事件一到，就打印i，而等到事件发生时，i早就变成的定值5，应为i是外层函数的i

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