m (integer > 2) which gives the start of the search (m inclusive)

n (integer >= m) which gives the end of the search (n inclusive)

That's in the kata's description, so (1, 1, 10) is not a valid input

if you want to get prime numbers with 1 gap between 1 and 10 ( "gap(1, 1, 10)" ) it should return [2,3] but it will return [1,2] and 1 is not a prime number. So you should add another verification in the isPrime function whereas if i == 1 return false

Spoiler flag, please.

Nice.

We can change
j < i
to
Math.sqrt(i) + 1
in isPrime method.

This is indeed correct, thanks for noticing! I've amended my code to recognise 1 as not prime and include 4 in the prime checks. This is submitted as a new solution here:
https://www.codewars.com/kata/reviews/561eaaf5353ce442ad00004d/groups/5b43601cff888b9e620030d6

Unfortunately, I don't know how to change this particular code here...

The isPrime method recogniyes 1 and 4 as prime numbers.

last = i;Very clever