If you have completed the Tribonacci sequence kata, you would know by now that mister Fibonacci has at least a bigger brother. If not, give it a quick look to get how things work.

tribonacci.js

// Well, time to expand the family a little more: think of a Quadribonacci starting with a signature of 4 elements and each following element is the sum of the 4 previous, a Pentabonacci (well Cinquebonacci would probably sound a bit more italian, but it would also sound really awful) with a signature of 5 elements and each following element is the sum of the 5 previous, and so on.

// Well, guess what? You have to build a Xbonacci function that takes a signature of X elements - and remember each next element is the sum of the last X elements - and returns the first n elements of the so seeded sequence.

// xbonacci {1,1,1,1} 10 = {1,1,1,1,4,7,13,25,49,94}
// xbonacci {0,0,0,0,1} 10 = {0,0,0,0,1,1,2,4,8,16}
// xbonacci {1,0,0,0,0,0,1} 10 = {1,0,0,0,0,0,1,2,3,6}
// xbonacci {1,1} produces the Fibonacci sequence

function Xbonacci(signature, n){
	var tempArr = signature.slice(0);
	const reducer = (accumulator, currentValue) => accumulator + currentValue;
  
  // Looping through.
	for (var i=1; i<=n; i++) {
    // Get Last n elements.
		var lastnEl = tempArr.slice(-signature.length);
    // Pushing it to new arr.
		tempArr.push(lastnEl.reduce(reducer));
	}
	return tempArr.slice(0, n);
}