README.md

Infinity Scroll with response validation

A small project that implements the functionality of content loading by scroll and validation of the response from the slicer

Technologies Used 🛠️

Key features 🔑

• Infinite scrolling using the custom useIntersection hook.
• Data validation using the Zod library.
• Error handling via ErrorBoundary component.
• Universal API class for working with requests.

Description 👾

PostsList is the main React component of the project, implementing infinite scrolling to display a list of posts using the Intersection Observer API. The component includes a clever architecture for data processing, validation of the response from the API, and robust error handling.

Core functionality 🧠

API class

The project uses an abstract API class for unified API handling.

Features

• Base URL: Set once when the child class is initialized.

• Response validation: Each response is validated through a Zod schema to ensure that the data is correct.

• Method fetcher: Universal method for executing HTTP requests.

• Error Management: A detailed error message is generated if the data structure is incorrect.

API response validation

• Each data upload is rigorously validated through Zod.

• PostSchema and PostsSchema schemas are used to ensure that the response structure is as expected.

• If the data is not valid, the request is terminated with an error, which helps avoid incorrect data display.

Infinite scrolling with useIntersection

• The useIntersection hook uses IntersectionObserver to track the intersection of an item (ref to “cursor” at the end of the list) with the viewing area.

• Once the user reaches the end of the list, the fetchNextPagePostList colback is triggered.

• Implemented automatic unsubscribe via observer.disconnect() when the tracked item is unmounted or changed.

Data loading

• When the component is first rendered, the first page of posts is loaded.

• Further loading occurs automatically when the end of the list is reached.

Loading States

• If data is being loaded, the user sees the Loading.... message

• Once the data is successfully loaded, it is rendered on the page.

Working with API

• The useGetPostList hook controls request states (load, successful completion, errors).

• Data is loaded page by page via the fetchNextPage method.

Error handling

• The project uses ErrorBoundary component for safe operation of the application. It intercepts errors and displays a friendly message to the user.

Dynamic rendering

• The list of posts is represented as cards (PostCard), each of which displays data from the API.

How it works? 🚀

API Class

• API class basic structure:

  export abstract class API {
  protected baseUrl: string;
  
  constructor(baseUrl: string) {
    this.baseUrl = baseUrl;
  }
  protected async fetcher<T extends z.ZodTypeAny>({
    endpoint,
    options,
    schema,
    schemaName,
  }: FetcherParams<T>): Promise<z.infer<T>> {
    const response = await fetch(`${this.baseUrl}${endpoint}`, options);
  
    if (!response.ok) {
      throw new Error(`Request failed with status ${response.status}`);
    }
  
    const data = await response.json();
    const validationResult = schema.safeParse(data);
  
    if (!validationResult.success) {
      console.error(`Validation error in ${schemaName}:`, validationResult.error);
      throw new Error(`Invalid response for ${schemaName}`);
    }
  
    return validationResult.data;
    }
  }

Advantages

• Unification of query logic.

• Centralized error handling and validation.

• Easy extensibility for creating new API classes.

Data validation via Zod

• All data from the API is validated using schemas:

  • PostSchema: ensures that the post object contains userId, id, title and body fields with valid types.

  • PostsSchema: validates an array of PostSchema objects.

• This reduces the chance of errors due to incorrect data.

useIntersection

• The useIntersection structure:

  const useIntersection = (onIntersect: () => void) => {
    const unsubscribe = useRef(() => {});
    return useCallback(
      (element: HTMLDivElement | null) => {
        const observer = new IntersectionObserver(entries => {
          entries.forEach(intersection => {
            if (intersection.isIntersecting) {
              onIntersect();
            }
          });
        });
  
        if (element) {
          observer.observe(element);
          unsubscribe.current = () => observer.disconnect();
        } else {
          unsubscribe.current();
        }
      },
      []
    );
  };

• The useIntersection hook uses IntersectionObserver to track the intersection of an item (ref to “cursor” at the end of the list) with the viewport.

• Automatically unsubscribe via observer.disconnect() when the tracked item is unmounted or changed.

• Universal interface for use in all lazy loading scenarios.