JavaScript 用户名验证

Question

对于本作业，我必须编写代码来检查用户名是否有效(如下所示)，但如果前两个警报存在，最后一个警报将如何显示？

    function isUserNameValid(user) {
    "use strict";
    var alert = "";
    if (user.length > 12) {
    alert("cannot be more than 12 letters long");
    return false;
  }
    alert = /^[A-Za-z]+$/;
    if (!alert.test(user)) {
    alert("must only use letters A-Z or a-z");
    return false;
  }
    alert = /^[A-Za-z]+$/;     //<--(this part is the question?)
    if(user.length > 12 || if(!alert.test(user)) {
    alert("must only use letters A-Z or a-z and cannot be more than 12 letters long)";
    return false;
 }
return true;
}

Answer 1

将 if 放在前面，然后将其余两个放在后面

if(user.length > 12 && if(!a.test(user)) {   
 alert("must only use letters A-Z or a-z and cannot be more than 12 letters long)";   return false; 
}