What’s new in React 16.3(.0-alpha)

React is a popular JavaScript library for building user interfaces. With the release of version 16.3(.0-alpha), React has introduced some exciting new features and improvements that will make it easier to build even more complex and powerful web applications.

Context API

One of the most significant changes in React 16.3 is the introduction of the new Context API. This API allows you to pass data down through the component tree without having to use props at every level. It simplifies the process of sharing data between components that are not directly related.

Context provides a way to share values like colors, themes, or user authentication information across a React component hierarchy, without having to explicitly pass a prop through every level. In other words, you can create a context object in one place and then use it anywhere in the component tree.

Here's an example of how to use the Context API:

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In this example, the ThemeContext object is created using the createContext method. Then, the App component wraps the Toolbar component with the ThemeContext.Provider, which passes the value "dark" to any children consuming the ThemeContext. Finally, the ThemedButton component uses the static contextType property to access the ThemeContext value and apply it to the button's theme.

Lifecycle Changes

React 16.3 also introduces some changes to component lifecycle methods.

New Methods

Two new lifecycle methods have been added: getDerivedStateFromProps() and getSnapshotBeforeUpdate(). These methods are called during the updating phase, before render(), and provide a way to update state based on changes to props or to capture information about the DOM before it's updated.

Here's an example of how to use getDerivedStateFromProps():

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In this example, the MyComponent class defines the getDerivedStateFromProps() method, which checks whether the props.value has changed since the last time it was called. If so, it updates the component's state with the new value.

Deprecated Methods

Two lifecycle methods have been deprecated in React 16.3: componentWillReceiveProps() and componentWillUpdate(). These methods will continue to work in version 16.3 but will be removed in a future release, so you should update your code to use the new methods instead.

Other Changes

React 16.3 also includes some other improvements and changes, including:

• A new forwardRef() API that makes it easier to pass refs through intermediate components.
• Better support for returning null from render() to indicate a "null" state.
• Improvements to the ErrorBoundary API.
• Support for returning arrays of elements from render().

Conclusion

React 16.3 introduces some exciting new features and improvements that make it easier to build complex and powerful web applications. The new Context API simplifies the process of sharing data between components, while the new lifecycle methods provide more control over how components update. These changes will help developers build better React applications and improve the overall user experience.

If you are working on a React project, it's worth taking the time to learn about these new features and incorporate them into your code. By doing so, you can take advantage of the latest advances in React and create even better web applications.

来源：JavaScript中文网 ，转载请注明来源 https://www.javascriptcn.com/post/6718