multiWaysMerge.js

/*
 * time complexity = O(n)
 */
function twoWayMerge (arr1, arr2) {
	if (!arr1 || !arr2) {
		return 'illegal params'
	}
	
	if (arr1.length === 0 || arr2.length === 0) {
		return arr1.concat(arr2)
	}

	const result = []
	let i = 0, j = 0

	while (i < arr1.length && j < arr2.length) {
		if(arr1[i] <= arr2[j]) {
			result.push(arr1[i])
			i++
		} else {
			result.push(arr2[j])
			j++
		}
	}

	if (i > arr1.length - 1) {
		result.push(...arr2.slice(j))
	} else {
		result.push(...arr1.slice(i))
	}

	return result
}

/*
 * time complexity = O(n*(k-1))
 */
function multiWaysMerge (...args) {
	return args.reduce(twoWayMerge)
}

multiWaysMerge([0, 2, 4, 6, 8], [0, 2, 3, 5, 7], [0, 2, 4, 6, 8], [0, 2, 3, 5, 7], [0, 2, 4, 6, 8], [0, 2, 3, 5, 7])

@lansana yeah，you're right.