Function createInputSignal

packages/core/src/authoring/input/input_signal.ts:115–151

(
  initialValue: T,
  options?: InputOptions<T, TransformT>,
)

 * @param options Additional options for the input. e.g. a transform, or an alias.
 */
export function createInputSignal<T, TransformT>(
  initialValue: T,
  options?: InputOptions<T, TransformT>,
): InputSignalWithTransform<T, TransformT> {
  const node: InputSignalNode<T, TransformT> = Object.create(INPUT_SIGNAL_NODE);

  node.value = initialValue;

  // Perf note: Always set `transformFn` here to ensure that `node` always
  // has the same v8 class shape, allowing monomorphic reads on input signals.
  node.transformFn = options?.transform;

  function inputValueFn() {
    // Record that someone looked at this signal.
    producerAccessed(node);

    if (node.value === REQUIRED_UNSET_VALUE) {
      let message: string | null = null;
      if (ngDevMode) {
        const name = options?.debugName ?? options?.alias;
        message = `Input${name ? ` "${name}"` : ''} is required but no value is available yet.`;
      }
      throw new RuntimeError(RuntimeErrorCode.REQUIRED_INPUT_NO_VALUE, message);
    }

    return node.value;
  }

  (inputValueFn as any)[SIGNAL] = node;

  if (ngDevMode) {
    inputValueFn.toString = () => `[Input Signal: ${inputValueFn()}]`;
    node.debugName = options?.debugName;
  }

  return inputValueFn as InputSignalWithTransform<T, TransformT>;
}