recursive-sum.js

const someArray = [4,3,3,2,5,6,63,1,43,34,46,46,2,35,35,64,75];

function sum(list) {
	let count = 1;

	function add(x,y) {
		const sum = x + y;

		if(++count > list.length - 1) {
			return sum;
		}

		return add(sum, list[count]);
	}

	return add(list[0], list[1]);
}

const result = sum(someArray);

console.log(result);