Recently I was digging into some repository and my attention was caught by this code:

const nowInSeconds = ~~(Date.now() / 1000)

What the heck are doing the tilde there?

I had to google it and of course ended up in Stack Overflow

It behaves like that:

~N -> -(N+1)

A couple of examples

~-2 --> 1
~2 --> -3

Why the heck would i need something like this in a normal context?

yes.. i know that you can write clever hacks to convert falsy values or determine if you found something when using indexOf (~ -1 is 0, thus false)... but what are we even talking about?

You can use it, to convert any floating point number to a integer without performance overkill that comes with Math.floor(). Additionally, when you care about minification of your code, you end up using 2 characters (2 tildes) instead of 12. (from JS bitwise operators in practice)

Should we really use ~~(a/b) to avoid writing Math.floor(a/b)? Are you kidding me?

Honestly, when used in a normal application, in simple methods that are not running thousands of operation per second, it just hides the intention and hinders readability.
You might argue that it is just a matter of habit and I could be as well complain about the Spread Operator - in comparison to Object.assign:

const mergedOptions = {...optionsDefault, ...options};

const mergedOptions  = Object.assign({}, optionsDefault, options);

and you might be true. But sorry, no, it is not the same thing.

These micro-optimisation using bitwise operator, are most of the time unnecessary tricks to look smarter during code reviews.

Welcome to the cult

Just imagine this hypothetical conversation:

Oh, you really didn't know the double tilde? C'mon! it's a bitwise operation ( pronounced with low mysterious emphatic tone - welcome to the cult!) and it's sooo much faster than Math.floor.
Me: oh.. really? how much faster?
Up to 30% faster!!!
Me: wow, but, how much do we gain in milliseconds?
you can bring down 100000 operation from 44ms to 28s!!!!
Me: besides the fact who's gonna notice 20 milliseconds less in our application anyway, we are NOT running 100.000 operations! we are just running Math.floor ONCE at start-up!!! Get outta here!

I am not saying it is not useful. it definitely is, under some circumstances.
But as for any optimisation, we should do them when they are needed and they make sense.

Otherwise, keep it simple and favour readability.

some other useful resources about the topic:

Clever coding tricks ( that we don't need )

Welcome to the cult