的Javascript用戶名驗證

Question

對於這個功課我必須寫檢查，如果被有效如下所示用戶名密碼，但如何將最後警告一下，如果前兩個警示存在嗎？

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

把第一，如果下面和兩個

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; 
}