js 正则表达式验证邮箱事例

if(email.value.length!=0)   {     if (email.value.charAt(0)=="." ||                  email.value.charAt(0)=="@"||                 email.value.indexOf('@', 0) == -1 ||           email.value.indexOf('.', 0) == -1 ||           email.value.lastIndexOf("@")==email.value.length-1 ||           email.value.lastIndexOf(".")==email.value.length-1)      {       alert("Email地址格式不正确！");       email.focus();       return false;       }    }else   {    alert("Email不能为空！");    email.focus();    return false;    }