Javascript function for email validation does not enter Else

Question

Can someone tell me why that function can’t get into else?

When the email meets the function it usually works only when it does nothing, ie the function recognizes that the condition of the if is not true, but still does not enter the else:

function isValidEmail(email) {

    var regEmail = /^[\w.\+]+@\w+.\w{2,}(?:.\w{2})?$/gmi;

    email.replace(regEmail, function(match){
        if(match === email){
            alert('Email válido');
        }else{      
            alert('Email inválido');    
        }
    });     
}

Answer 1

The function replace is for making replacements. In this case, it uses regex to fetch a snippet of the string, which you can replace with another (and this other snippet may include the return of a function). Use this function as a way to check whether the regex has given match it is like using a drill to tighten a screw (it may even work sometimes, but...)

How well remembered in the reply from @Sam, to function is called only when the regex finds a match. When the email is invalid, it is not even executed, which is another reason not to "screw with the drill".

In this case, you just want to know if a string matches regex, then you can use test(), returning true or false (if the string matches regex or not):

let reg = /^[\w.\+]+@\w+.\w{2,}(?:.\w{2})?$/;

function isValidEmail(email){
  return reg.test(email);
}

console.log(isValidEmail('[email protected]')); // true
console.log(isValidEmail('abc')); // false

The detail is that I removed the flags g, m and i, because you don’t have to.

The g causes the regex to keep the content of the last match found and continue from there (as per described in the documentation), which causes if the first match is found, the second match is done from the end of the string (since the regex ends with $, that corresponds to the end of the string). As you are always searching from the beginning (^) at the end ($) string, do not need this option.

The m activates the mode multiline, but I believe it is not necessary because an email address has no line breaks.

And the i activates the mode case insensitive (does not differentiate between upper and lower case). But as \w already takes both upper and lower case letters, this option is not required.

In fact, I wouldn’t even need function, you can call test straightforward:

let reg = /^[\w.\+]+@\w+.\w{2,}(?:.\w{2})?$/;

if (reg.test('[email protected]')) {
  alert("Email válido");
} else {
  alert("Email inválido");
}

---

About validation of emails with regex

About using regex to validate emails, I talk in more detail in this answer.

Just to summarize, emails are more complex than they seem and a regex to validate any email it’s very complicated.

Your regex, for example, starts with [\w.\+], which means she considers the emails below valid:

let reg = /^[\w.\+]+@\w+.\w{2,}(?:.\w{2})?$/;

function isValidEmail(email){
  return reg.test(email);
}

console.log(isValidEmail('....@_.com')); // true
console.log(isValidEmail('...@__.11')); // true
console.log(isValidEmail('++_+@ab.__')); // true

This happens because the brackets define a character class: they take whatever character is inside them. In case, [\w.\+] means:

• one \w (capital letters, lower case letters, numbers, or _), or
• a point (.), or
• a sign of more (+)

Then there is the quantifier +, which means "one or more occurrences", i.e., [\w.\+]+ accepts several points or several +, or several _ - see here examples of this particular working excerpt.

The same goes for the rest of the regex (mainly the \w, than by accepting _, ends up validating the above cases).

It is up to you to decide whether you will live with these false positives, or go on complicating your regex more and more, until you get to that:

let reg = /^[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?$/;

console.log(reg.test("[email protected]")); // true
console.log(reg.test("abc")); // false
console.log(reg.test("....@_.com")); // false
console.log(reg.test("...@__.11")); // false
console.log(reg.test("++_+@ab.__")); // false

Or that:

let reg = /^(([^<>()[\]\\.,;:\s@\"]+(\.[^<>()[\]\\.,;:\s@\"]+)*)|(\".+\"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/;

console.log(reg.test("[email protected]")); // true
console.log(reg.test("abc")); // false
console.log(reg.test("....@_.com")); // false
console.log(reg.test("...@__.11")); // false
console.log(reg.test("++_+@ab.__")); // false

Or that - I confess that I did not even have the courage to test, but it is below as reference:

(?:(?:\r\n)?[ \t])*(?:(?:(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t]
)+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:
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?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ 
\t]))*"(?:(?:\r\n)?[ \t])*))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\0
31]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\
](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+
(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:
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|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)
?[ \t])*)*\<(?:(?:\r\n)?[ \t])*(?:@(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\
r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[
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:\r\n)?[ \t])*))*\>(?:(?:\r\n)?[ \t])*)|(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?
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:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[
\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*|(?:[^()<>@,;:\\".\[\] \000-
\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(
?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)*\<(?:(?:\r\n)?[ \t])*(?:@(?:[^()<>@,;
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.\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\
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".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)(?:\.(?:(
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 \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,
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)*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\
".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*)*:(?:(?:\r\n)?[ \t])*)?
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\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)(?:\.(?:(?:
\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\[
"()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])
*))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])
+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\
.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z
|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*\>(?:(
?:\r\n)?[ \t])*))*)?;\s*)

Answer 2

The Function replace does not check conditions at the validation level because the function will only be executed if replace has found any occurrence.

You can use conditions if in the replace Function?

Yes, but only with what was found, and not with what was not found. In this case you can do whatever you want with what was combined in replace.

In the example below, I can tell if the email sent to the function was exactly as expected:

function isValidEmail(email) {

    var regEmail = /^[\w.\+]+@\w+.\w{2,}(?:.\w{2})?$/gmi;

    return email.replace(regEmail, function(match){
        if(match === "[email protected]"){
            return 'email válido';
        }else{      
            return 'Email inválido';
        }
    });     
}
console.log(isValidEmail("[email protected]"));
console.log(isValidEmail("[email protected]"));

In your case, if supposedly the email is invalid according to the proposed regex (without entering the merit of the quality of this regex, already well served in the hkotsubo response), replace will not be met and consequently the function will not be executed, because the function replace does not work as a callback.

replace is not used for validations, but to make substitutions according to combinations found (see documentation) or return some kind of treatment within the replace found.