jQuery源码的一些写法

NO1

减少window查找时间和保护undefined变量,压缩时将undefined压缩成u，字节数减少

(function(window,undefined){
    undefined=2;
    alert(undefined);
})(window);

结果会是弹出2

undefined=2;
alert(undefined);

结果会弹出undefined

NO2

为了得到jQuery原型链上的方法

(function(window,undefiend){
    var jQuery=function(select,context){
        return new jQuery.fn.init(select,context);
    }
    jQuery.fn=jQuery.prototype={
        init:function(selector,context){

        }
    }
    jQuery.fn.init.prototype=jQuery.fn;
})(window);

jQuery插件扩展

jQuery.fn.extend({
    a:function(){
        console.log(123);
    }
});
$('').a(); //123
jQuery.extend({
    s:13
});
jQuery.s; //13

NO3

开始时$(".text")不存在，把事件都绑定到body上

$('body').append('<div class="text"></div>');
$('body).on('click','test',function(){

});

NO4

$('.test').val()取值，$('.test').val('test')赋值

function addMethod(obj,name,f){
    //老的还是undefined
    var old=obj[name];
    //people[find]=function,给people加find方法
    obj[name]=function(){
        //f.length为find0传递过来的参数，此时find0没传参数所以为0，
        //arguments.length为实参是people.find()穿的实参，所以为0.
        if(f.length===arguments.length){
            //f为find0，this是把people的指向f，f具有people的一些属性
            return f.apply(this,arguments);
        }else{
        
            return old.apply(this,arguments);
        }
    }
}
var people={
    name:["zhangsan","lisi","wangerma"]
}
var find0=function(){
    return this.name;
}
addMethod(people,'find',find0);
people.find();

function addMethod(obj,name,f){
    //old undefined obj.find->find0
    //old find0     obj.find->find1
    var old=obj[name];
    obj[name]=function(){
        if(f.length===arguments.length){
            return f.apply(this,arguments);
        }else{
            return old.apply(this,arguments);
        }
    }
}
var people={
    name:["zhangsan","lisi","wangerma"]
}
var find0=function(){
    return this.name;
}
var find1=function(name){
    var arr=this.name;
    for(var i=0;i<=arr.length;i++){
        if(arr[i]==name){
            return arr[i]+'在'+i+'位';
        }
    }
}
addMethod(people,'find',find0);
addMethod(people,'find',find1);
console.log(people.find('lisi'));
console.log(people.find());
        

执行结果

lisi在1位
 (3) ["zhangsan", "lisi", "wangerma"]

NO5

if(a){
    var foo=a;
}else{
    var foo=b;
}

//短路表达式
var foo=a||b;
 
a&&test()

NO6

勾子

$.each("Boolean Number String Function Array Date RegExp Object Error".split(""),function(i,name){
    class3type["[object"+name+"]"]=name.toLowerCase();
});

>Object.prototype.toString.call({})
>"[object Object]"
>Object.prototype.toString.call([])
>"[object Array]"

NO7

onready

var $=ready=window.ready=function(fn){
            if(document.addEventListener){//兼容非IE
                document.addEventListener('DOMContentLoaded',function(){
                    //注销事件，避免反复触发
                    document.removeEventListener('DOMContentLoaded',arguments.callee,false);
            fn();//调用参数函数
        },false);
    }else if(document.attachEvent){//IE
        IEContentLoaded(window,fn);
    }
    function IEcontentLoaded(w,fn){
        var d=w.document,done=false;
        init=function(){
            if(!done){
                done=true;
                fn();
            }
        }
        //polling for no errors
        (function(){
            try{
                //throws errors until after ondocumentready
                d.documentElement.doScroll('left');
            }catch(e){
                setTimeout(arguments.callee,50);
                return;
            }
            init();
        })();
    }
}