largestRunningSum.js

const largestRunningSum = (inputArr = []) => {
  let runningSum = 0;
  let maxSum = 0;
  
  inputArr.forEach(item => {
    runningSum += item;
    
    if (runningSum > 0 && runningSum > maxSum) {
      maxSum = runningSum;
    } else if (runningSum < 0) {
      runningSum = 0;
    }
  });
  
  return maxSum;
};

console.log('largestRunningSum([-1, 1, -2])', largestRunningSum([-1, 1, -2])); //returns 1;
console.log('largestRunningSum([4, -1, 3, -6, -10])', largestRunningSum([4, -1, 3, -6, -10])); //returns 6;
console.log('largestRunningSum([1, 2, -3, 6, 4])', largestRunningSum([1, 2, -3, 6, 4])); //returns 6;