I don't understand javascript

Need help understanding the using !!fooBar vs fooBar when checking ?(truthiness?) I'm not sure what is being checked.

I'm used to seeing the latter fooBar.

Both evaluate truthyness, but the first one explicitely "casts" it into a bool

E.g.

let notEmpty = someString; // notEmpty is a string

let notEmpty = !!someString; // notEmpty is a bool

If used in an if condition or with other boolean operators it doesn't matter since they automatically coerce it into a bool

JS haxx0rs love obfuscation so they'd rather use this than typing fooBar.isEmpty or something similarly readable.

It probably comes from a C programmer.

It was used when you wanted to cast a "bool" (C does not have bool) into either a 0 or a 1.

Technically true is any nonzero integer, but you could do some nifty math tricks by doing the !! And thus ensuring true would be 1 and not just any nonzero.

!!booBar is Boolean(fooBar)

@kiki Oh, darling, if !!booBar is your take on Boolean(fooBar), then your coding logic's as revolutionary as rediscovering the semicolon.

@princess semicolons are for dinosaurs

This reminds me of the +'a' in banana

@Lensflare fun fact, my dad have a semi colon. We had to remove half of it when he had a rectocolisis at 24. Dark shit, he literally puked poo at some point.

most JS complaints come from specific nitpicking. You don't need to use double ! if you hate it. I personally use strictly boolean variable for this kind of purpose, even though JS itself allows us to reassign it any other kind of data.