function log(i){ return console.log(i); } 

    function $ (id)
    {
        if(typeof id === "string"){
            return document.getElementById(id);
        }else{
            return id;
        }
    }
    function PicList(){
        this.elem = $(arguments[0]);
        this.arr = [];
        var iTarget = [
            { left:0 },
            { left:50 },
            { left:100 },
            { left:150 },
            { left:200 }
        ];
        
        this.run();
    }
    PicList.prototype.run = function(){
        log(this.elem)  //null
    }
    Animate.prototype = new PicList("wrap");
    function Animate(){
        log(this.arr)
    }
    var obj = new Animate();
//HTML
<div id="wrap">    </div>