JohnnyDiabetes, you make a good point. If I made this today I'd do a few things differently, one of which would be to create a new array and return that.

Just a heads up:

Kata directions: "Do not mutate the input array/list." This solution mutates the input array.

The *= is a multiplication assignment and can be read the same away as array[i] = array[i] * -1. It is a shorthand solution that often gets used when solving problems.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Multiplication_assignment

Hi begginner here, how does it works? I mean, I wrote the same thinks but how could it works on the negative numbers? Because the positine ones get to negatives thanks to * -1, I get it; but does it work for the negatives one? Maybe it's the "=" that's I don't understand here. Sorry for my bad english, hope someone will understand my question.