Boolean object is not working properly in condition

Question

I´m really confused. Maybe anyone can help me? The problem is the following:

var isSignInside = new Boolean(someCondition);

if (!isSignInside) {
    //doStuff
}
else {
    //doOtherStuff
}

Now, if isSignInside is false (the debugger told me), the script still jumps to //doOtherStuff. How can this be? The rest of the snippet isn´t of relevance, but I can share it if asked. Surely there is an easy explanation i don´t see. Thanks in advance. Edit: The someCondition really is a custom method "forced" to return a bool instead of (otherwise) a string. Edit: Just used the function directly in the if. Needed some tricky paranthesis, but works now. Thanks for the hint that a (boolean) object can never be === to a static boolean primitive. Hell this forum is fast.

`new Boolean()` creates an object, and object is always going to be true. you just need to check your condition directly.. eg. `if (!someCondition)` — Keith, Aug 24 '17 at 14:15
The very first example in https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Boolean describies exactly this case. — Oleg Estekhin, Aug 24 '17 at 14:15
funny title, javascript never works actually, browsers do it (or don't) — Kaddath, Aug 24 '17 at 14:16
tl;dr do `Boolean(someCondition)` instead of `new Boolean(someCondition)` — Damon, Aug 24 '17 at 14:17
Try `if (isSignInside + 0)`. The `+ 0` will force the Boolean object to be coerced to its primitive value. — , Aug 24 '17 at 14:20

Pointy · Answer 1 · 2017-08-24T14:15:18.573

4

When you create a Boolean object, it's an object. A reference to it, regardless of the boolean primitive value it represents, will always test as truthy just like any other non-null object reference.

There's generally no point in constructing a Boolean instance like that:

var isSignInside = !!someCondition;

That'll give you a boolean primitive that reflects the truthy/falsy state of your condition.

edited Aug 24 '17 at 14:15

answered Aug 24 '17 at 14:14

Pointy

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your answer would be better if you explained how to make the code work in addition to explaining why it won't. – Bryan Oakley Aug 24 '17 at 14:15
This is the correct answer but you might want to expand on it so OP can understand – Damon Aug 24 '17 at 14:15
@BryanOakley done – Pointy Aug 24 '17 at 14:15
it is also common to use `Boolean(someCondition)` – Damon Aug 24 '17 at 14:15
No, i also tried === false. Didn´t work either. – L. Riemer Aug 24 '17 at 14:16
@Damon yes that'd work too but I don't like typing :) – Pointy Aug 24 '17 at 14:16
1

@L.Riemer that's because no object reference is `===` to the boolean primitive constant `false`. – Pointy Aug 24 '17 at 14:16
never seen any reason to use Boolean object, and this post doesn't convince to ever use it :P well, i guess there are rare cases.. – Kaddath Aug 24 '17 at 14:19

score 2 · Answer 2 · answered Aug 24 '17 at 14:17

2

if(new Boolean(false)) alert("hehe");

Actually, isSignedInside is not a boolean, but a boolean object (thanks to the new). You may want to get its primitive value for comparison:

if( (new Boolean(false)).valueOf() ) alert("hehe");

Or even easier, take the value directly.

answered Aug 24 '17 at 14:17

Jonas Wilms

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Visualizing same concept from debugger: http://imgur.com/a/zRbUb – Xaqron Aug 24 '17 at 14:22

score 1 · Answer 3 · answered Aug 24 '17 at 14:18

1

Well that's not how that's done. You want to use a boolean primitive. What you're trying to do is done this way:

var isSignInside = (someCondition);
if (isSignInside === false) {
   //doStuff
}
else {
    //doOtherStuff
}

https://jsfiddle.net/catbadger/pxrteq59/

answered Aug 24 '17 at 14:18

catbadger

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No. Negating it is probably better then strict equality to false – Jonas Wilms Aug 24 '17 at 14:40
That´s the point. As i just learned `!(new Boolean(false))` does evaluate to false. – L. Riemer Aug 24 '17 at 14:48
@Jonasw defend your statement. negation is ambiguous – catbadger Aug 24 '17 at 14:59
@catbager !isSignedIn – Jonas Wilms Aug 24 '17 at 15:03
that is ambiguous. if it's not equal to false but zero, your statement will evaluate to true. – catbadger Aug 24 '17 at 15:27

Boolean object is not working properly in condition

3 Answers3