简单封装js的dom查询实例代码

$ = function (val) {    switch(val.charAt(0)) {      case '#' :        return document.getElementById(val.substring(1));        break;      case '.' :        val = val.replace('.','');        if(document.getElementsByClassName)          return document.getElementsByClassName(val);        else {          var obj = document.getElementsByTagName('*'),len = obj.length,arr=[];          for(var i=0;i<len;i++) {            if(obj[i].className == val) {              arr[arr.length] = obj[i];            }          }          return arr;        }        break;      default :        if(document.getElementsByName(val).length > 0)          return document.getElementsByName(val);        else           return document.getElementsByTagName(val);     }  }