js原生 获取url参数

function GetQueryString(name) {
   var reg = new RegExp("(^|&)" + name + "=([^&]*)(&|$)", "i");
   var r = window.location.search.substr(1).match(reg);
   var context = "";
   if (r != null)
      context = r[2];
   reg = null;
   r = null;
   return context == null || context == "" || context == "undefined" ? "" : context;
}