Method update

src/Map.js:483–555

(ownerID, shift, keyHash, key, value, didChangeSize, didAlter)

  }

  update(ownerID, shift, keyHash, key, value, didChangeSize, didAlter) {
    if (keyHash === undefined) {
      keyHash = hash(key);
    }

    const removed = value === NOT_SET;

    if (keyHash !== this.keyHash) {
      if (removed) {
        return this;
      }
      SetRef(didAlter);
      SetRef(didChangeSize);
      return mergeIntoNode(this, ownerID, shift, keyHash, [key, value]);
    }

    const entries = this.entries;
    const len = entries.length;
    const isEditable = ownerID && ownerID === this.ownerID;
    const foundIdx = this._positionOf(key, isEditable);
    const idx = foundIdx === -1 ? len : foundIdx;
    const exists = foundIdx !== -1;

    if (exists ? entries[idx][1] === value : removed) {
      return this;
    }

    SetRef(didAlter);
    // eslint-disable-next-line @typescript-eslint/no-unused-expressions -- TODO enable eslint here
    (removed || !exists) && SetRef(didChangeSize);

    if (removed && len === 2) {
      return new ValueNode(ownerID, this.keyHash, entries[idx ^ 1]);
    }

    const newEntries = isEditable ? entries : arrCopy(entries);

    if (exists) {
      if (removed) {
        // eslint-disable-next-line @typescript-eslint/no-unused-expressions -- TODO enable eslint here
        idx === len - 1
          ? newEntries.pop()
          : (newEntries[idx] = newEntries.pop());
        // The swap-pop reshuffles positions; drop the stale index (rebuilt lazily).
        if (isEditable) {
          this._index = undefined;
        }
      } else {
        // Same key, same position: the index stays valid.
        newEntries[idx] = [key, value];
      }
    } else {
      newEntries.push([key, value]);
      // Keep the index in sync on the transient insert path. Persistent inserts
      // return a fresh node below whose index rebuilds lazily, so skip them.
      if (isEditable && this._index !== undefined) {
        const secondaryHash = hashCollisionKey(key);
        const positions = this._index[secondaryHash];