Course overview

How to work with course materials

Introduction

Setting up Developer Environment

Setting up Initial Project

How to Use ESLint and Prettier Together in a React Project

How to Configure React to Use TypeScript

How to Add Jest to a React Project for Automated Testing

Setting up developer environment

Building React Hooks: API Considerations and Best Practices

How to Implement a Custom useBoolean React Hook

Testing a Custom useBoolean Hook With React Testing Library

How to Implement a Custom useMap Hook With Tests

How to Quickly Import Custom React Hooks With an Index File

Implement an Object Returning API With a react-hanger Clone

Development of custom hooks

CommonJS vs ES6: An Intro to JavaScript Module Systems

What is Transpilation? An Intro to Transpilers vs Compilers

An Intro to Transpilers: ESBuild, Babel, and SWC Compared

What are Babel Transforms and Plugins?

A Beginner's Guide to JavaScript Bundlers

How to Simplify Bundling React Code With Microbundle

How to Add TypeScript Build Steps to React

How to Implement Babel Build Steps in a React App

Conclusion

Preparing code for publishing

Add Continuous Integration to a React Build With GitHub Actions

How to Automatically Generate a React App Changelog

How to Publish a React Library to NPM With GitHub Actions

Publishing the Code

In this course we’ll build a set of custom reusable hooks, a mini react-hanger clone, essentially going from nothing to a fully-automated publishing pipeline that follows the best practices.  We will cover common Hooks APIs every React developer should know, then dive straight into implementing Custom React Hooks, similar to what you will find in leading React libraries in the open source React ecosystem.

## Why this course
React Hooks promise to eliminate the difficulties of sharing state without writing class-based components. The challenge is that Hooks do away with the lifecycle methods and class-based semantics of state management that many React developers were familiar with.  Learning React Hooks on your own can be time consuming, confusing and frustrating.  With that in mind, The newline Guide to Creating a React Hooks Library, was created to provide a complete tutorial that fully covers React Hooks.  Within a few hours you'll have a strong grasp on React Hooks and how to implement them.

## Course Topics
This course packs practical hands-on-instruction using and building React Hooks, along with the best practices you need to build wider React Hooks libraries others across your organization can use.
The first module provides an overview of the React Hooks library project we’ll build, and we'll set up a complete environment with tools for library development.
The subsequent modules then take you through building with React Hooks and creating your React Hooks library, including:
- Hooks API fundamentals
- Developing custom React Hooks
- How to write reusable React Hooks
- Common React Hooks mistakes to avoid in your code
- Transpilers and bundlers for JavaScript libraries
- Using GitHub Actions to test, build, and lint your library
- Publish your React Hooks library to NPM

We’ll use tools including React, TypeScript, Babel, as well as GitHub Actions to build, test, and package a React Hooks library available for others to download from NPM.  Ultimately, build your own React Hooks library and learn the best practices that will make your code reusable. With these skills, you can contribute more confidently to any React codebase using React Hooks, and make your team more productive.

This course is a complete step-by-step guide to coding custom React Hooks and building a Hooks library from scratch.  Confidently master React Hooks, a transformative update added since React version 16.8, that makes it much easier to reuse code as your React codebase grows.

The newline Guide to Creating a React Hooks Library

Common React Hooks mistakes to avoid in your code

Transpilers and bundlers for JavaScript libraries

Using GitHub Actions to test, build, and lint your library

This time around we will implement a hook named 

, that will wrap around a native Map object and mimic its API. We're going to start with the tests this time.

The same logic applies. We want the actions that will change our state to stay the same no matter the changes of the state. In other words, only changes to the state should trigger
a re-render of a component that gets state as a prop.

We'll start with the imports and test cases. For this, it's good to open the 

We don't care about the reading part, we care about writing, because we need to create a new instance of the map in order to make it immutable to change. So we need 

 action in order to clear and override the whole map with fresh data in one go, which can be useful in some use cases.

---
title: How to Implement a Custom useMap Hook With Tests
isPublicLesson: false
privateVideoUrl: https://fullstack.wistia.com/medias/cjsdbbsg2x
code: https://gitlab.com/fullstackio/books/newline-course-apps/andrey-los-newline-guide-to-creating-a-react-hooks-library-app/-/tree/main/code/module_03/lesson_03.04/App?ref_type=heads
---

This time around we will implement a hook named `useMap`, that will wrap around a native Map object and mimic its API. We're going to start with the tests this time.

The same logic applies. We want the actions that will change our state to stay the same no matter the changes of the state. In other words, only changes to the state should trigger
a re-render of a component that gets state as a prop.

We'll start with the imports and test cases. For this, it's good to open the [MDN documentation](https://developer.mozilla.org/ru/docs/Web/JavaScript/Reference/Global_Objects/Map) on `Map` prototype and its methods.

We don't care about the reading part, we care about writing, because we need to create a new instance of the map in order to make it immutable to change. So we need `delete`, `clear` and `set`. Also in `react-hanger` I have added `initialize` action in order to clear and override the whole map with fresh data in one go, which can be useful in some use cases.

So let's create the `useMap.test.ts` file alongside our other tests.

// Walk through while writing the code

```ts
import { act, renderHook } from "@testing-library/react-hooks";
import { useMap } from "../useMap";

describe("useMap array", () => {
  describe("set", () => {
    it("should update old value", () => {});
    it("should add new value", () => {});
  });

  describe("delete", () => {
    it("should delete existing value", () => {});
  });

  describe("initialize", () => {
    it.each`
      message    | input
      ${"map"}   | ${new Map([[1, "initialized"]])}
      ${"tuple"} | ${[[1, "initialized"]]}
    `("initializes with $message", ({ input }) => {});
  });

  describe("clear", () => {
    it("clears the map state and gets values", () => {});
  });

  describe("hooks optimizations", () => {
    it("should change value reference equality after change", () => {});
    it("should keep actions reference equality after value change", () => {});
  });
});
```

Essentially we can just copy and paste a little bit of code from the `useBoolean` test and adjust it a bit to save some typing. Thanks to the magic of editing I'll quickly type it all in, and explain it line-by-line after each case.

// Quick walk through each case

```ts
import { act, renderHook } from "@testing-library/react-hooks";
import { useMap } from "../useMap";

describe("useMap array", () => {
  describe("set", () => {
    it("should update old value", () => {
      // given
      const { result } = renderHook(() => useMap<number, string>([[1, "default"]]));
      const [, actions] = result.current;
      expect(result.current[0].get(1)).toBe("default");
      // when
      act(() => actions.set(1, "changed"));
      // then
      expect(result.current[0].get(1)).toBe("changed");
    });
    it("should add new value", () => {
      // given
      const { result } = renderHook(() => useMap<number, string>());
      const [, actions] = result.current;
      expect(result.current[0].get(1)).toBeUndefined();
      // when
      act(() => actions.set(1, "added"));
      // then
      expect(result.current[0].get(1)).toBe("added");
    });
  });