I knew this in and out, but as a Full-Stack PHP/Symfony/Frontend/JS guy who pivoted to mainly TS for b2b stuff, I still have to occasionally enter

!""

into the browser console just to be sure, during code reviews :D

▲ tredre3 2 hours ago | parent [-]

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.

	▲	moritzwarhier 2 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` is `true`