Method removeBefore

src/List.js:301–335

(ownerID, level, index)

  // TODO: seems like these methods are very similar

  removeBefore(ownerID, level, index) {
    if (
      (index & ((1 << (level + SHIFT)) - 1)) === 0 ||
      this.array.length === 0
    ) {
      return this;
    }
    const originIndex = (index >>> level) & MASK;
    if (originIndex >= this.array.length) {
      return new VNode([], ownerID);
    }
    const removingFirst = originIndex === 0;
    let newChild;
    if (level > 0) {
      const oldChild = this.array[originIndex];
      newChild =
        oldChild && oldChild.removeBefore(ownerID, level - SHIFT, index);
      if (newChild === oldChild && removingFirst) {
        return this;
      }
    }
    if (removingFirst && !newChild) {
      return this;
    }
    const editable = editableVNode(this, ownerID);
    if (!removingFirst) {
      for (let ii = 0; ii < originIndex; ii++) {
        editable.array[ii] = undefined;
      }
    }
    if (newChild) {
      editable.array[originIndex] = newChild;
    }
    return editable;
  }

  removeAfter(ownerID, level, index) {
    if (