js-高级技术

高级技术：

1、function Person(name,age,job){

this.name=name;

this.age=age;

this.job=job;

}

var person=new Person("zhng",20,"zzzz");

var person=Person("zhng",20,"zzzz"); ---this指的是window对象

2、在使用大量if条件语句的时候：

function createXHR(){

if(typeOf XMLHttpRequest != "undefined"){

createXHR=function(){

return new XMLHttpRequest();

};

}else if(typeOf ActiveXObject !=undefined){

createXHR=function(){

if(typeOf arguments.callee.activeXString !="string"){

var version=["MSXML2.XMLHttp.6.0","MSXML2.XMLHttp.3.0","MSXML2.XMLHttp"],

i,len;

for(i=0,len=versions.length;i<len;i++){

try{

new ActiveXObject(versions[i]);

arguments.callee.activeXString=versions[i];

break;

}catch(ex){

//skip

}

}

}

return new ActiveXObject(arguments.callee.activeXString);

};

}else{

createXHR=function(){

throw new Error("NO XHR object available.");

};

}

return createXHR();

}

If语句的每个分支都会为createXHR变量赋值，有效覆盖了原有的函数。

3、函数绑定

var handler={

message:"event handler",

handlerClick:function(event){

alert(this.message);

}

};

var btn=document.getElementById("my-btn");

EventUtil.addHandler(btn,"click",function(event){

handler.handlerClick(event);

})

EventUtil.addHandler(btn,"click",bind(handler.handlerClick,handler));

EventUtil.addHandler(btn,"click",handler.handlerClick.bind(handler));

4、防篡改的对象：

不可扩展对象：

var person={name:"zhang"};

//不能再给对象添加属性以及方法

object.preventExtensions(person);

person.age=29;

alert(person.age); //undefined

密封的对象：

var person={name:"zhang"};

//不能再给对象删除属性以及方法

object.seal(person);

person.age=29;

alert(person.age); //undefined

delete person.name;

alert(person.name); //zhang

冻结的对象

var person={name:"zhang"};

//既不可扩展也密封

object.freeze(person);

person.age=29;

alert(person.age); //undefined

delete person.name;

alert(person.name); //zhang

person.name="hui";

alert(person.name);//zhang

5、拖放：为了元素能够拖放，必须是绝对定位

var DragDrop=function(){

var dragging=null;

diffX=0;

diffY=0;

function handleEvent(event){

//获取事件和目标

event=EventUtil.getEvent(event);

var target=EventUtil.getTarget(event);

//确定事件类型

switch(event.type){

case "mousedown":

if(target.className.indexOf("draggable")>-1){

dragging=target;

diffX=event.clientX-target.offsetLeft;

diffY=event.clientY-target.offsetTop;

}break;

case "mousemove":

if(dragging!=null){

//指定位置

dragging.style.left=(event.clientX-diffX)+"px";

dragging.style.top=(event.clientY-diffY)+"px";

}break;

case "mouseup":

dragging=null;

break;

}

};

return {

enable:function(){

EventUtil.addHandler(document,"mousedown",handleEvent);

EventUtil.addHandler(document,"mousemove",handleEvent);

EventUtil.addHandler(document,"mouseup",handleEvent);

},

disable:function(){

EventUtil.addHandler(document,"mousedown",handleEvent);

EventUtil.addHandler(document,"mousemove",handleEvent);

EventUtil.addHandler(document,"mouseup",handleEvent);

}

}

}();