原生js取得id,tagName,class

//  id 

        this.$ = function(id) {

            return document.getElementById(id);

        };



        //  

        this.$$ = function(tagName, parent) {

            parent = parent || document;

            return parent.getElementsByTagName(tagName);

        };



        //  

        this.$Class = function(className, parent) {

            var arr = [], result = [];

            parent = parent || document;

            arr = this.$$("*");

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

                if ((" " + arr[i].className + " ").indexOf(" " + className + " ") > 0) {

                    result.push(arr[i]);

                }

            }

            return result;

        };