Angular应用的依赖注入调试

上下文：我实现了一个hero service，在其构造函数里添加了一些打印语句：

在另一个Component的构造函数里将其注入：

运行时，观察service构造函数如何被调用的：

function getNodeInjectable(lView, tView, index, tNode) {
    let value = lView[index];
    const tData = tView.data;
    if (isFactory(value)) {
        const factory = value;
        if (factory.resolving) {
            throw new Error(`Circular dep for ${stringifyForError(tData[index])}`);
        }
        const previousIncludeViewProviders = setIncludeViewProviders(factory.canSeeViewProviders);
        factory.resolving = true;
        let previousInjectImplementation;
        if (factory.injectImpl) {
            previousInjectImplementation = setInjectImplementation(factory.injectImpl);
        }
        enterDI(lView, tNode);
        try {
            value = lView[index] = factory.factory(undefined, tData, lView, tNode);
            // This code path is hit for both directives and providers.
            // For perf reasons, we want to avoid searching for hooks on providers.
            // It does no harm to try (the hooks just won't exist), but the extra
            // checks are unnecessary and this is a hot path. So we check to see
            // if the index of the dependency is in the directive range for this
            // tNode. If it's not, we know it's a provider and skip hook registration.
            if (tView.firstCreatePass && index >= tNode.directiveStart) {
                ngDevMode && assertDirectiveDef(tData[index]);
                registerPreOrderHooks(index, tData[index], tView);
            }
        }
        finally {
            if (factory.injectImpl)
                setInjectImplementation(previousInjectImplementation);
            setIncludeViewProviders(previousIncludeViewProviders);
            factory.resolving = false;
            leaveDI();
        }
    }
    return value;
}