JS: Get placeholder index

index.js

/**
 * Get placeholder index, like for example in a list, through node top offset.
 * Used for drag-n-drops.
 *
 * @param {number} y The actual top offset
 * @param {number} scroll Scroll count
 * @return {number}
 */
function getPlaceholderIndex(y, scroll) {
  const height = 70;
  const margin = 20;

  if (y < height / 2) {
    return 0;
  }

  // Just a little explanation why:
  // In general, you use the formula `y / height = offset`.
  // However, `y` always starts from where the card was dragged,
  // thus `(y / (height / 2)) / height`.
  return Math.floor((y - (height / 2)) / (height + margin));
}