const tapeEquilibrium = function(array) {
  let leftSum = array[0];
  let rightSum = array[array.length-1];
  if (array.length < 3) {
    return Math.abs(leftSum - rightSum);
  }
  let leftIndex = 1;
  let rightIndex = array.length-2;
  while (leftIndex <= rightIndex) {
    let leftElement = array[leftIndex];
    let rightElement = array[rightIndex];
    let newLeftSum = leftSum + leftElement;
    let newRightSum = rightSum + rightElement;
    let differenceAddingToLeft = Math.abs(newLeftSum - rightSum);
    let differenceAddingToRight = Math.abs(leftSum - newRightSum);
    if (differenceAddingToLeft <= differenceAddingToRight) {
      leftSum = newLeftSum;
      leftIndex++;
    } else {
      rightSum = newRightSum;
      rightIndex--;
    }
  }
  return Math.abs(leftSum - rightSum);
}

tapeEquilibrium([3,1,2,4,3]) === 1;
tapeEquilibrium([3,-100,2,4,3]) === 94;
tapeEquilibrium([3,-100]) === 103;
tapeEquilibrium([-99,1000,-100]) === 999;