array.ts

/* Silently ignores nonsense reorders! */
export function moveArrayItem(item: unknown, array: unknown[], direction: 'up' | 'down'): void {
  const oldIndex = array.indexOf(item);

  if ((array.length > 1) &&
    !(direction === 'down' && oldIndex + 1 === array.length) && // dont allow last element down
    !(direction === 'up' && oldIndex === 0)) { // dont allow first element up
    const newIndex = direction === 'up' ? oldIndex - 1 : oldIndex + 1;
    const elements = array.splice(oldIndex, 1);
    array.splice(newIndex, 0, elements[0]);
  }
}