for(type in{Top:"",Left:""})这句是什么意思，坐等大神讲解

Question

(function(){
function k(a,b,c){
        if(a.addEventListener)
a.addEventListener(b,c,false);
else a.attachEvent&&a.attachEvent("on"+b,c)
}
function g(a){
        if(typeof window.onload!="function")
window.onload=a;
        else{
            var b=window.onload;
            window.onload=function(){
                b();
                a()
                }
            }
    }
function h(){
    var a={};
    
    for(type in{Top:"",Left:""}){
        var b=type=="Top"?"Y":"X";
        if(typeof window["page"+b+"Offset"]!="undefined")a[type.toLowerCase()]=window["page"+b+"Offset"];
        else{
            b=document.documentElement.clientHeight?document.documentElement:document.body;
            a[type.toLowerCase()]=b["scroll"+type]
            }
        }
    return a
}
function l(){
    var a=document.body,b;
    if(window.innerHeight)b=window.innerHeight;
    else if(a.parentElement.clientHeight)b=a.parentElement.clientHeight;
    else if(a&&a.clientHeight)b=a.clientHeight;
    return b
    }
function i(a){
    this.parent=document.body;
    this.createEl(this.parent,a);
    this.size=Math.random()*5+5;
    this.el.style.width=Math.round(this.size)+"px";
    this.el.style.height=Math.round(this.size)+"px";
    this.maxLeft=document.body.offsetWidth-this.size;
    this.maxTop=document.body.offsetHeight- this.size;
    this.left=Math.random()*this.maxLeft;
    this.top=h().top+1;
    this.angle=1.4+0.2*Math.random();
    this.minAngle=1.4;
    this.maxAngle=1.6;
    this.angleDelta=0.01*Math.random();
    this.speed=2+Math.random()
    }
var j=false;
g(function(){
    j=true
    });
var f=true;
window.createSnow=function(a,b){
    if(j){
        var c=[],m=setInterval(function(){
            f&&b>c.length&&Math.random()<b*0.0025&&c.push(new i(a));
            !f&&!c.length&&clearInterval(m);
            for(var e=h().top,n=l(),d=c.length-1;d>=0;d--)if(c[d])if(c[d].top<e||c[d].top+c[d].size+1>e+n){
                c[d].remove();
                c[d]=null;
                c.splice(d,1)
                }else{
                c[d].move();
                c[d].draw()
                }
            },40);
    k(window,"scroll",function(){
        for(var e=c.length-1;e>=0;e--)c[e].draw()
            })
    }else g(function(){
    createSnow(a,b)
    })
};window.removeSnow=function(){
    f=false
    };
    
i.prototype={
    createEl:function(a,b){
        this.el=document.createElement("img");
        this.el.setAttribute("src",b+"snow"+Math.floor(Math.random()*4)+".gif");
        this.el.style.position="absolute";
        this.el.style.display="block";
        this.el.style.zIndex="99999";
        this.parent.appendChild(this.el)
        },
    move:function(){
        if(this.angle< this.minAngle||this.angle>this.maxAngle)this.angleDelta=-this.angleDelta;
        this.angle+=this.angleDelta;
        this.left+=this.speed*Math.cos(this.angle*Math.PI);
        this.top-=this.speed*Math.sin(this.angle*Math.PI);
        if(this.left<0)this.left=this.maxLeft;
        else if(this.left>this.maxLeft)this.left=0
            },
    draw:function(){
        this.el.style.top=Math.round(this.top)+"px";
        this.el.style.left=Math.round(this.left)+"px"
        },
    remove:function(){
        this.parent.removeChild(this.el);
        this.parent=this.el=null
        }
    }
})();下雪图里面
 for(type in{Top:"",Left:""}){
        var b=type=="Top"?"Y":"X";
        if(typeof window["page"+b+"Offset"]!="undefined")a[type.toLowerCase()]=window["page"+b+"Offset"];
        else{
            b=document.documentElement.clientHeight?document.documentElement:document.body;
            a[type.toLowerCase()]=b["scroll"+type]
            }
        }
    return a
}
Top:"",Left:""这句是什么意思？

Answer 1

就是json的格式 var obj = {a: 1, b: 1};
alert(obj.a) // 1
var obj = {a: '', b: 1};
alert(obj.a) // 空字符