Finding the contiguous/continuous subarray of an array argument with the maximal sum of items

getMaxSubSumFast.js

// Fast:
function getMaxSubSum(arr) {
  let maxSum = 0;
  let partialSum = 0;

  for (let item of arr) { // for each item of arr
    partialSum += item; // add it to partialSum
    maxSum = Math.max(maxSum, partialSum); // remember the maximum
    if (partialSum < 0) partialSum = 0; // zero if negative
  }

  return maxSum;
}

getMaxSubSumSlow.js

// Slow:
function getMaxSubSum(arr) {
	let maxSum = 0;

	for (let i = 0; i < arr.length; i++) {

		let sumFixedStart = 0;

		for (let j = i; j < arr.length; j++) {
			sumFixedStart += arr[j];
			maxSum = Math.max(maxSum, sumFixedStart);
		}
	}

	return maxSum;
}