Function ɵɵdeferWhen

packages/core/src/defer/instructions.ts:231–262

(rawValue: unknown)

 * @codeGenApi
 */
export function ɵɵdeferWhen(rawValue: unknown) {
  const lView = getLView();
  const tNode = getSelectedTNode();

  if (ngDevMode) {
    trackTriggerForDebugging(lView[TVIEW], tNode, 'when <expression>');
  }

  if (!shouldAttachTrigger(TriggerType.Regular, lView, tNode)) return;

  const bindingIndex = nextBindingIndex();
  if (bindingUpdated(lView, bindingIndex, rawValue)) {
    const prevConsumer = setActiveConsumer(null);
    try {
      const value = Boolean(rawValue); // handle truthy or falsy values
      const lDetails = getLDeferBlockDetails(lView, tNode);
      const renderedState = lDetails[DEFER_BLOCK_STATE];
      if (value === false && renderedState === DeferBlockInternalState.Initial) {
        // If nothing is rendered yet, render a placeholder (if defined).
        renderPlaceholder(lView, tNode);
      } else if (
        value === true &&
        (renderedState === DeferBlockInternalState.Initial ||
          renderedState === DeferBlockState.Placeholder)
      ) {
        triggerDeferBlock(TriggerType.Regular, lView, tNode);
      }
    } finally {
      setActiveConsumer(prevConsumer);
    }
  }
}

/**
 * Prefetches the deferred content when a value becomes truthy.