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); 
    }
  }