Class FieldNode

packages/forms/signals/src/field/node.ts:73–511

 * the responsibilities.
 */
export class FieldNode implements FieldState<unknown> {
  readonly structure: FieldNodeStructure;
  readonly validationState: ValidationState;
  readonly metadataState: FieldMetadataState;
  readonly nodeState: FieldNodeState;
  readonly submitState: FieldSubmitState;
  readonly fieldAdapter: FieldAdapter;
  readonly controlValue: ControlValueSignal<unknown>;

  private _context: FieldContext<unknown> | undefined = undefined;
  get context(): FieldContext<unknown> {
    return (this._context ??= new FieldNodeContext(this));
  }

  /**
   * Proxy to this node which allows navigation of the form graph below it.
   */
  readonly fieldProxy = new Proxy(() => this, FIELD_PROXY_HANDLER) as unknown as FieldTree<any>;
  private readonly pathNode: FieldPathNode;

  constructor(options: FieldNodeOptions) {
    this.pathNode = options.pathNode;
    this.fieldAdapter = options.fieldAdapter;
    this.structure = this.fieldAdapter.createStructure(this, options);
    this.validationState = this.fieldAdapter.createValidationState(this, options);
    this.nodeState = this.fieldAdapter.createNodeState(this, options);
    this.metadataState = new FieldMetadataState(this);
    this.submitState = new FieldSubmitState(this);
    this.controlValue = this.controlValueSignal();
    // We eagerly create metadata at the end of construction so that the node is fully constructed
    // before metadata creation logic runs (which may access other states on the node).
    this.metadataState.runMetadataCreateLifecycle();
  }

  focusBoundControl(options?: FocusOptions): void {
    this.getBindingForFocus()?.focus(options);
  }

  /**
   * Gets the Field directive binding that should be focused when the developer calls
   * `focusBoundControl` on this node.
   *
   * This will prioritize focusable bindings to this node, and if multiple exist, it will return
   * the first one in the DOM. If no focusable bindings exist on this node, it will return the
   * first focusable binding in the DOM for any descendant node of this one.
   */
  private getBindingForFocus():
    | (FormField<unknown> & {focus: (options?: FocusOptions) => void})
    | undefined {
    // First try to focus one of our own bindings.
    const own = this.formFieldBindings()
      .filter(
        (b): b is FormField<unknown> & {focus: (options?: FocusOptions) => void} =>
          b.focus !== undefined,
      )
      .reduce(
        firstInDom<FormField<unknown> & {focus: (options?: FocusOptions) => void}>,
        undefined,