What does !() mean in javascript

Question

I just saw this construction for the first time in javascript

if (someConditionIsMet && !(anotherCondition && oneMoreCondition)) {
  return something
}

There is a !() inside of the if-conditional statement. I'm wondering what exactly that does. Is it just a way of grouping several conditions together and making sure they all evaluate a certain way before triggering logic? If so, is this merely to simplify the appearance or is there some logical advantage here?

Answer 1

Specifically for !(anotherCondition && oneMoreCondition), it means NOT (anotherCondition AND oneMoreCondition).

This is De Morgan's laws:

not (A and B) = not A or not B

Some might say that not A or not B is easier to read than not (A and B) but that's personal preference.

Expanding the whole condition using De Morgan's law would result in:

someConditionIsMet AND (NOT anotherCondition OR NOT oneMoreCondition)

in Javascript:

if (someConditionIsMet && (!anotherCondition || !oneMoreCondition))

You can use that expanded form if you think it's more readable.

Answer 2

!() In any case in javascript means that if they are NOT true. So basically like in this case...

if(!(anotherCondition && oneMoreCondition)) {
Console.log("If both set to false this would run!");
}

if anotherCondition and oneMoreCondition were both set to false this would actually return true. This here might help you: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Logical_Operators#Logical_NOT_!

Answer 3

It's evaluating the condition of anotherCondition && oneMoreCondition, and then reversing it.

So if the condition evaluates to true, the ! makes the condition evaluate to false.