without diving too much, looks like there must be a shorter way to define the game result.

Hmm... I don't like this kata.

after looking on the instructions I don't get how this case should equal 19

sumIntervals( [
   [1, 5],
   [10, 20],
   [1, 6],
   [16, 19],
   [5, 11]
] ) => 19

which ones overlap each other here?

Clearly, [10, 20] and [16, 19] overlapping one another. So it gives, 10.

To me, all 3 others overlap each other so it's like [1, 11], which gives 10 as well.

As a result, shouldn't I get 20 here?

Skipping this one for now.

Should I write a function to convert an output a sum of two numbers (which is 9.100232822049192e+28) to become a full number without a scientific notation? Is it a main idea? Or it is supposed to convert arguments firstly, i.e. to be displayed as an entire numbers without notation, and then sum up them?

yep, got it now, thx!

say we have ')))))(((((', so the n equals to 0 too, doesnt it?