Check values in a form (Javascript)

Question

I've five variables in a form, for simplicity I named them A, B, C, D and E. In order to submit the form (A or (B or C)) and (D or E) must have a value (I hope it's clear :P). I've tried with

if ((A == "" || (B == "" || C == "")) && (D == "" || E == "")) {
    alert ("Error!");
} else {
    form.submit();
}

But it doesn't work in every case. For example, if A, B and C have a value, the form is submitted even if neither D or E have values. Thank you for the help!

I am thinking your or logic is wrong.... Thinking you want some ANDs and not ORs. — epascarello
– epascarello, Commented Aug 22, 2017 at 18:35
If you're using this code to validate a form you should consider trimming the string value and then checking if the length is greater than 0 (or compare it against an empty string like you're doing). This way a user can't enter a bunch of blank spaces to circumvent your validation. Unless you're already formatting the values before you store them in A, B, C, D, E. — Tom O.
– Tom O., Commented Aug 22, 2017 at 23:55

Community · Accepted Answer · 2020-06-20 09:12:55Z

2

If you have all strings, you could just reverse the condition and check all with logical AND and one OR.

var a = '', b = '', c = '', d = '', e = '';
    
if (a && b && c || d && e) {
    console.log('form.submit();');
} else {
    console.log('Error!');
}

Why it works:

given
(A == "" || (B == "" || C == "")) && (D == "" || E == "")
simplified A == "" is equivalent to !A
(A == "" || B == "" || C == "") && (D == "" || E == "")

(!A || !B || !C) && (!D || !E)
De Morgan's laws !(a && b) = !a || !b or !(a || b) = !a && !b
 (!A || !B || !C) && (!D || !E)

 !(A &&  B &&  C) && !(D &&  E)

!((A &&  B &&  C) ||  (D &&  E))
operator precedence
!(A && B && C || D && E)
now switch/negate then <-> else
A && B && C || D && E

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Aug 22, 2017 at 18:38

Nina Scholz

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3 Comments

clabe45 Over a year ago

That's the not the logic that the OP has provided.

Nina Scholz Over a year ago

actually its the same logic, just negated.

clabe45 Over a year ago

So you don't need the parenthesis with AND in this case?

Sushanth -- · Accepted Answer · 2017-08-22 18:39:13Z

1

if (A == "" || B == "" || C == "" && (D == "" || E == "")) {
        alert ("Error!");
} else {
       form.submit();
}

edited Aug 22, 2017 at 18:39

Sushanth --

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answered Aug 22, 2017 at 18:38

Victor Vieira

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Comments

clabe45 · Accepted Answer · 2017-08-23 12:09:18Z

1

You need to change your logic to:

if ((A != "" || (B != "" || C != ""))
    && (D != "" || E != "")) {
        form.submit();
} else {
       alert ("Error!");
}

The alternative is to do it like so:

if ((A == "" && (B == "" && C == ""))
    || (D == "" && E == "")) {
        alert ("Error!");
} else {
      form.submit();
}

Edit: the first snippet can be refactored to the following:

if ((A || (B || C )) && (D || E )) {
        form.submit();
} else {
       alert ("Error!");
}

And the same can be done with the second snippet with the NOT operator !.

edited Aug 23, 2017 at 12:09

answered Aug 22, 2017 at 18:36

clabe45

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3 Comments

Abozanona Over a year ago

alert ("Error!");

Dylan Wright Over a year ago

The only thing I'd add would be instead of using the == operator use the === operator, this checks value and type, unless type doesn't matter. Another discussion, but should be considered.

clabe45 Over a year ago

@DylanWright, the variables are guaranteed to be strings, since they are input values.

Tom O. · Accepted Answer · 2017-08-22 23:45:35Z

0

I updated the code a bit. I think this should work for you.

function isNonEmpty(string) {
  //returning the string's truthiness value
  return string.trim() ? true : false;
}

//change these values around to make sure the logic is correct
var A = "cat",
  B = "    ",
  C = "dog",
  D = "",
  E = " turtle";

//almost exactly what you have just calling a function for neatness
if ((isNonEmpty(A) || isNonEmpty(B) || isNonEmpty(C)) &&
  (isNonEmpty(D) || isNonEmpty(E))) {
  console.log("Valid form. Time to submit!");
} else {
  console.log("Invalid form. Please check your values!");
}

edited Aug 22, 2017 at 23:45

answered Aug 22, 2017 at 18:48

Tom O.

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