function Trim(str)
   { 
    return str.replace(/(^\s*)|(\s*$)/g, ""); 
  }

  function Trim(str,is_global)
  {
   var result;
   result = str.replace(/(^\s+)|(\s+$)/g,"");
   if(is_global.toLowerCase()=="g")
   {
    result = result.replace(/\s/g,"");
    }
   return result;
}

if (!String.prototype.trim) {

 /*---------------------------------------
  * 清除字符串两端空格，包含换行符、制表符
  *---------------------------------------*/
 String.prototype.trim = function () { 
  return this.triml().trimr(); 
 }

 /*----------------------------------------
  * 清除字符串左侧空格，包含换行符、制表符
  * ---------------------------------------*/
 String.prototype.triml = function () {
  return this.replace(/^[\s\n\t]+/g, "");
 }

 /*----------------------------------------
  * 清除字符串右侧空格，包含换行符、制表符
  *----------------------------------------*/
 String.prototype.trimr = function () {
  return this.replace(/[\s\n\t]+$/g, "");
 }
}

if (!String.prototype.trim){

 /*---------------------------------------
  * 清除字符串两端空格，包含换行符、制表符
  *---------------------------------------*/
 String.prototype.trim = function () { 
  return this.replace(/(^[\s\n\t]+|[\s\n\t]+$)/g, "");
 }
 
}

var str = " abcd ".trim();