Function transformedValue

packages/forms/signals/src/api/transformed_value.ts:122–158

(
  value: ModelSignal<TValue>,
  options: TransformedValueOptions<TValue, TRaw>,
)

 */
export function transformedValue<TValue, TRaw>(
  value: ModelSignal<TValue>,
  options: TransformedValueOptions<TValue, TRaw>,
): TransformedValueSignal<TRaw> {
  const {parse, format} = options;
  const parser = createParser(value, value.set, parse);

  // Create the result signal with overridden set/update and a `parseErrors` property.
  const rawValue = linkedSignal(() => format(value()));
  const result = rawValue as WritableSignal<TRaw> & {
    parseErrors: Signal<readonly ValidationError.WithoutFieldTree[]>;
  };
  result.parseErrors = parser.errors;
  const originalSet = result.set.bind(result);

  // Wire up the integration with the form control (parse errors and reset handling).
  const integration = inject(FORM_CONTROL_INTEGRATION, {self: true, optional: true});
  if (integration) {
    integration.setParseErrors(parser.errors);
    integration.onReset = (resetValue) => {
      parser.reset();
      const modelValue = resetValue !== undefined ? resetValue : value();
      originalSet(format(modelValue));
    };
  }

  // Notify the parser when `set` or `update` is called on the raw value
  result.set = (newRawValue: TRaw) => {
    parser.setRawValue(newRawValue);
    originalSet(newRawValue);
  };
  result.update = (updateFn: (value: TRaw) => TRaw) => {
    result.set(updateFn(rawValue()));
  };

  return result;
}