简单模拟jquery选择器

var aQuery = function(selector){
        //强制为对象
        if(!(this instanceof aQuery)){
            return new aQuery(selector)
        }
        var elem = document.getElementById(/[^#].*/.exec(selector)[0]);
        this.length = 1;
        this[0] = elem;
        this.context = document;
        this.selector = selector;
        this.get = function(num){
            return this[num];
        }
        return this
    }

既可通过aQuery("#book")[0] / aQuery("#book").get(0) 获取到元素