This release includes a new class component lifecycle (`getDerivedStateFromProps`), a new `StrictMode` component, and an official context API!
For the past few months, the React team has been working on support for asynchronous rendering. We are excited about the new features this will enable, and we've learned that some changes will be required to the way we write React components.
For the past few months, the React team has been working on support for [asynchronous rendering](#). We are excited about the new features this will enable, and we've learned that some changes will be required to the way we write React components.
We're releasing version 16.3 primarily so that open source maintainers can start incorporating these changes into their libraries well in advance of the next major release. **However, you should not feel pressured to make changes to your application code yet.** We respect semver and will not ship breaking changes in a minor version!
Read on to learn more about the release!
Read on to learn more about the release.
## Official Context API
For many years, React has offered an experimental API for context. Although it was a powerful tool, our advice was mostly to [avoid using it](/docs/context.html#why-not-to-use-context) because of potential problems with the API. We've always intended to replace the experimental API with a better one, and as of version 16.3- we've finally done that!
[Learn more about the new context API here.](#)
## Component Lifecycle Changes
React's class component API has been around for years with little change. However, as we add support for more advanced features (such as [error boundaries](/docs/react-component.html#componentdidcatch) and the upcoming async rendering mode) we stretch this model in ways that it was not originally intended.
React's class component API has been around for years with little change. However, as we add support for more advanced features (such as [error boundaries](/docs/react-component.html#componentdidcatch) and the upcoming [async rendering mode](#)) we stretch this model in ways that it was not originally intended.
For example, with the current API, it is too easy to block the initial render with non-essential logic. In part this is because there are too many ways to accomplish a given task, and it can be unclear which is best. We've observed that the interrupting behavior of error handling is often not taken into consideration and can result in memory leaks—(something that will also impact the upcoming async rendering mode). The current class component API also complicates other efforts, like our work on a React compiler.
For example, with the current API, it is too easy to block the initial render with non-essential logic. In part this is because there are too many ways to accomplish a given task, and it can be unclear which is best. We've observed that the interrupting behavior of error handling is often not taken into consideration and can result in memory leaks- (something that will also impact the upcoming async rendering mode). The current class component API also complicates other efforts, like our work on a React compiler.
Many of these issues are exacerbated by a subset of the component lifecycles (`componentWillMount`, `componentWillReceiveProps`, and `componentWillUpdate`). These also happen to be the lifecycles that cause the most confusion within the React community. For these reasons, we are going to deprecate those methods in favor of better alternatives.
Many of these issues are exacerbated by a subset of the component lifecycles (`componentWillMount`, `componentWillReceiveProps`, and `componentWillUpdate`). For this reason, we have decided to deprecate those methods.
We recognize that this change will impact many existing components. (At Facebook, we maintain more than 50,000 React components, and we can't tell our engineers to rewrite them either.) Because of this, the migration path will be as gradual as possible, and will provide escape hatches.
> **Note:**
>
> Deprecation warnings will be enabled in version 16.4, **but the deprecated lifecycles will continue to work until version 17**. After version 17, only the new "UNSAFE_" lifecycles will work.
> Deprecation warnings will be enabled in version 16.4, **but the deprecated lifecycles will continue to work until version 17**.
>
> After version 17, it will still be possible to use them, but they will be aliased with an "UNSAFE_" prefix to indicate that they might cause issues. We have also prepared an [automated script to rename them](https://github.com/reactjs/react-codemod#rename-unsafe-lifecycles) in existing code.
We are also adding a new static lifecycle, `getDerivedStateFromProps`, to replace the deprecated `componentWillReceiveProps`.
We are also adding a new static lifecycle, `getDerivedStateFromProps`, as a safer alternative to the deprecated `componentWillReceiveProps`.
[Learn more about these lifecycle changes here.](#)
@ -36,14 +46,8 @@ We are also adding a new static lifecycle, `getDerivedStateFromProps`, to replac
>
> `StrictMode` checks are run in development mode only; they do not impact the production build.
Although it is not possible for strict mode to catch all problems (eg mutation), it can help with many. If you see warnings in strict mode, those things will likely cause bugs for async rendering.
Although it is not possible for strict mode to catch all problems (e.g. certain types of mutation), it can help with many. If you see warnings in strict mode, those things will likely cause bugs for async rendering.
In version 16.3, `StrictMode` helps with two things: identifying unsafe lifecycles and detecting unexpected side effects. Additional functionality will be added with future releases of React.
[Learn more about the `StrictMode` component here.](#)
## Official Context API
For many years, React has offered an experimental API for context. Although it was a powerful tool, our advice was mostly to [avoid using it](/docs/context.html#why-not-to-use-context) because of potential problems with the API. We've always intended to replace the experimental API with a better one, and as of version 16.3- we've finally done that!
Brian Vaughn
7 years ago