请问在javascript语法中有类似于trim(字符串)这样的方法吗，即把字符串两头的空格去掉

function trim(str)
{
   return str.replace(/^s*|s*$/g,"");
}
var str = "  this is a test   ";

str = trim(str);

或是
   var str = "  this is a test   ";

   str = str.replace(/^s*|s*$/g,"");