Class TransientNode

frontend/lib/src/render-tree/TransientNode.ts:28–103

 */

export class TransientNode implements AppNode {
  readonly anchor?: AppNode
  readonly transientNodes: ElementNode[]
  readonly scriptRunId: string
  readonly deltaMsgReceivedAt?: number
  readonly fragmentId?: string
  readonly activeScriptHash?: string

  constructor(
    scriptRunId: string,
    anchor?: AppNode,
    transientNodes?: ElementNode[],
    deltaMsgReceivedAt?: number
  ) {
    this.scriptRunId = scriptRunId
    this.anchor = anchor
    this.transientNodes = transientNodes ?? []
    this.deltaMsgReceivedAt = deltaMsgReceivedAt ?? Date.now()

    // We explicitly set these to undefined because transient nodes
    // are not associated with a fragment or a script hash directly.
    // The anchor node will have the fragmentId and activeScriptHash.
    this.fragmentId = undefined
    this.activeScriptHash = undefined
  }

  /**
   * Updates the transient nodes by applying a function to each transient node.
   * If the function returns undefined, the transient node is removed from the list.
   * @param update - A function that takes an ElementNode and returns an ElementNode or undefined.
   * @returns A new array of transient nodes.
   */
  public updateTransientNodes(
    update: (node: ElementNode) => ElementNode | undefined
  ): ElementNode[] {
    const newTransientNodes: ElementNode[] = []
    this.transientNodes.forEach(element => {
      const updatedElement = update(element)
      if (updatedElement) {
        newTransientNodes.push(updatedElement)
      }
    })

    return newTransientNodes
  }

  accept<T>(visitor: AppNodeVisitor<T>): T {
    return visitor.visitTransientNode(this)
  }

  public debug(): string {
    return this.accept(new DebugVisitor())
  }

  // Combine the information of the node with the updated information
  // of *this* node
  public replaceTransientNodeWithSelf(node: TransientNode): AppNode {
    if (