React_Hooks v1.5.pdf: Chapter One & Two скачать в хорошем качестве

React_Hooks v1.5.pdf: Chapter One & Two

Based on common React Hooks learning resources such as the React Hooks Handbook and React Hooks in Action, the first two chapters typically cover foundational concepts. More information is available on the publisher's website. Hooks are a new addition in React 16.8. They let you use state and other React features without writing a class. This new function useState is the first “Hook” we’ll learn about, but this example is just a teaser. Don’t worry if it doesn’t make sense yet! You can start learning Hooks on the next page. On this page, we’ll continue by explaining why we’re adding Hooks to React and how they can help you write great applications. Video Introduction No Breaking Changes Before we continue, note that Hooks are: Completely opt-in. You can try Hooks in a few components without rewriting any existing code. But you don’t have to learn or use Hooks right now if you don’t want to. 100% backwards-compatible. Hooks don’t contain any breaking changes. Available now. Hooks are now available with the release of v16.8.0. There are no plans to remove classes from React. You can read more about the gradual adoption strategy for Hooks in the bottom section of this page. Hooks don’t replace your knowledge of React concepts. Instead, Hooks provide a more direct API to the React concepts you already know: props, state, context, refs, and lifecycle. As we will show later, Hooks also offer a new powerful way to combine them. If you just want to start learning Hooks, feel free to jump directly to the next page! You can also keep reading this page to learn more about why we’re adding Hooks, and how we’re going to start using them without rewriting our applications. Motivation Hooks solve a wide variety of seemingly unconnected problems in React that we’ve encountered over five years of writing and maintaining tens of thousands of components. Whether you’re learning React, use it daily, or even prefer a different library with a similar component model, you might recognize some of these problems. It’s hard to reuse stateful logic between components React doesn’t offer a way to “attach” reusable behavior to a component (for example, connecting it to a store). If you’ve worked with React for a while, you may be familiar with patterns like render props and higher-order components that try to solve this. But these patterns require you to restructure your components when you use them, which can be cumbersome and make code harder to follow. If you look at a typical React application in React DevTools, you will likely find a “wrapper hell” of components surrounded by layers of providers, consumers, higher-order components, render props, and other abstractions. While we could filter them out in DevTools, this points to a deeper underlying problem: React needs a better primitive for sharing stateful logic. With Hooks, you can extract stateful logic from a component so it can be tested independently and reused. Hooks allow you to reuse stateful logic without changing your component hierarchy. This makes it easy to share Hooks among many components or with the community. We’ll discuss this more in Building Your Own Hooks. Complex components become hard to understand We’ve often had to maintain components that started out simple but grew into an unmanageable mess of stateful logic and side effects. Each lifecycle method often contains a mix of unrelated logic. For example, components might perform some data fetching in componentDidMount and componentDidUpdate. However, the same componentDidMount method might also contain some unrelated logic that sets up event listeners, with cleanup performed in componentWillUnmount. Mutually related code that changes together gets split apart, but completely unrelated code ends up combined in a single method. This makes it too easy to introduce bugs and inconsistencies. In many cases it’s not possible to break these components into smaller ones because the stateful logic is all over the place. It’s also difficult to test them. This is one of the reasons many people prefer to combine React with a separate state management library. However, that often introduces too much abstraction, requires you to jump between different files, and makes reusing components more difficult. To solve this, Hooks let you split one component into smaller functions based on what pieces are related(such as setting up a subscription, fetching data), more than a split based lifecycle.