undefined

points

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In JS/TS:

    "0" == false : true
    ""  == false : true
    " " == false : true
    "1" == false : false

    !"0" : false
    !"" : true
    !" " : false
    !"1" : false

In PHP:

    "0" == false : true
    ""  == false : true
    " " == false : true
    "1" == false : false

    !"0" : true
    !"" : true
    !" " : false
    !"1" : false

Honestly the only way to remain sane in either, but especially if you use both, is to always use === and never use boolean logic (!) when a string could be involved.

by moritzwarhier2 hours ago|

parent|

[-]

That's what I say in code reviews as well. Same for numbers.

!someValue is useful only for:

- booleans, including optional booleans (which is why every bool flag should default to false)

- undefined, null (falsy), or object/function (truthy)

It's nice for the second variant to also cover falsy NaN or things like this, for example for forms.

I guess that's where

  !!""===false

comes from.

But it's this exact case that keeps tripping me up.

What about empty arrays?

Per my original comment, now I'd have to look up if

![]

is false in PHP, or just empty([]) === true

So yea I agree, and extend your case to PHP "arrays" (in JS,

  !![] === true

  true