code: function insert(queue, index, fns, mode = InsertMode.REGULAR) {
    fns.forEach(({ fn, name }) => {
      if (queue.findIndex(e => e.name === name) !== -1) {
        throw new Error(`${name}: A function is already queued with this name`);
      } else if (typeof fn !== 'function') {
        throw new Error(`${name}: Not a valid function`);
      }
    });
  
    const deleteCount = mode === InsertMode.REPLACE ? 1 : 0;
    queue.splice(index, deleteCount, ...fns);
  }
docs: Insert a bunch of functions into a queue at a given index.