Merge branch 'master' of https://github.com/reactjs/reactjs.org into defer-babel-loading

Author: renanpvaz

LICENSE-DOCS.md

@@ -8,8 +8,8 @@ This repo contains the source code and documentation powering [reactjs.org](http
 
 1. Git
 1. Node: install version 8.4 or greater
-1. Yarn: `npm i -g yarn` to install it globally via NPM
-1. A clone of the [reactjs.org repo](https://github.com/facebook/reactjs.org) on your local machine
+1. Yarn: See [Yarn website for installation instructions](https://yarnpkg.com/lang/en/docs/install/)
+1. A clone of the [reactjs.org repo](https://github.com/reactjs/reactjs.org) on your local machine
 1. A fork of the repo (for any contributions)
 
 ### Installation
@@ -26,7 +26,7 @@ This repo contains the source code and documentation powering [reactjs.org](http
 
 ### Create a branch
 
-1. `git checkout master` from any folder in your local react repository
+1. `git checkout master` from any folder in your local `reactjs.org` repository
 1. `git pull origin master` to ensure you have the latest main code
 1. `git checkout -b the-name-of-my-branch` (replacing `the-name-of-my-branch` with a suitable name) to create a branch
 
@@ -41,16 +41,16 @@ This repo contains the source code and documentation powering [reactjs.org](http
 ### Test the change
 
 1. If possible, test any visual changes in all latest versions of common browsers, on both desktop and mobile.
-1. Run `yarn check-all` from the project root. (This will run Prettier, ESlint, and Flow.)
+1. Run `yarn check-all` from the project root. (This will run Prettier, ESLint, and Flow.)
 
 ### Push it
 
 1. `git add -A && git commit -m "My message"` (replacing `My message` with a commit message, such as `Fixed header logo on Android`) to stage and commit your changes
 1. `git push my-fork-name the-name-of-my-branch`
-1. Go to the [reactjs.org repo](https://github.com/facebook/reactjs.org) and you should see recently pushed branches.
+1. Go to the [reactjs.org repo](https://github.com/reactjs/reactjs.org) and you should see recently pushed branches.
 1. Follow GitHub's instructions.
 1. If possible include screenshots of visual changes. A Netlify build will also be automatically created once you make your PR so other people can see your change.
 
 ## Troubleshooting
 
-- `yarn reset` to clear the local cache
+- `yarn reset` to clear the local cache

LICENSE.md

@@ -89,8 +89,8 @@ Therefore we decided not to have this built-in into React's class model. You can
 
 ```javascript
 class Counter extends React.Component {
-  constructor() {
-    super();
+  constructor(props) {
+    super(props);
     this.tick = this.tick.bind(this);
   }
   tick() {

README.md

@@ -79,11 +79,11 @@ We also encourage you to use JS error reporting services (or build your own) so
 
 React 16 prints all errors that occurred during rendering to the console in development, even if the application accidentally swallows them. In addition to the error message and the JavaScript stack, it also provides component stack traces. Now you can see where exactly in the component tree the failure has happened:
 
-<img src="../images/blog/error-boundaries-stack-trace.png" alt="Component stack traces in error message" style="width: 100%;">
+<img src="../images/docs/error-boundaries-stack-trace.png" alt="Component stack traces in error message" style="width: 100%;">
 
 You can also see the filenames and line numbers in the component stack trace. This works by default in [Create React App](https://github.com/facebookincubator/create-react-app) projects:
 
-<img src="../images/blog/error-boundaries-stack-trace-line-numbers.png" alt="Component stack traces with line numbers in error message" style="width: 100%;">
+<img src="../images/docs/error-boundaries-stack-trace-line-numbers.png" alt="Component stack traces with line numbers in error message" style="width: 100%;">
 
 If you don’t use Create React App, you can add [this plugin](https://www.npmjs.com/package/babel-plugin-transform-react-jsx-source) manually to your Babel configuration. Note that it’s intended only for development and **must be disabled in production**.
 

content/blog/2015-01-27-react-v0.13.0-beta-1.md

@@ -66,7 +66,7 @@ The [fbjs repository](https://github.com/facebook/fbjs) exists because React sha
 After cloning the [React repository](https://github.com/facebook/react), you will see a few top-level folders in it:
 
 * [`src`](https://github.com/facebook/react/tree/master/src) is the source code of React. **If your change is related to the code, `src` is where you'll spend most of your time.**
-* [`docs`](https://github.com/facebook/react/tree/master/docs) is the React documentation website. When you change APIs, make sure to update the relevant Markdown files.
+* [`docs`](https://github.com/reactjs/reactjs.org/tree/master/content) is the React documentation website. When you change APIs, make sure to update the relevant Markdown files.
 * [`fixtures`](https://github.com/facebook/react/tree/master/fixtures) contains a few small React test applications for contributors.
 * [`packages`](https://github.com/facebook/react/tree/master/packages) contains metadata (such as `package.json`) for all packages in the React repository. Nevertheless, their source code is still located inside [`src`](https://github.com/facebook/react/tree/master/src).
 * `build` is the build output of React. It is not in the repository but it will appear in your React clone after you [build it](/docs/how-to-contribute.html#development-workflow) for the first time.

content/blog/2017-07-26-error-handling-in-react-16.md

@@ -0,0 +1,137 @@
+---
+id: error-boundaries
+title: Error Boundaries
+permalink: docs/error-boundaries.html
+---
+
+In the past, JavaScript errors inside components used to corrupt React’s internal state and cause it to [emit](https://github.com/facebook/react/issues/4026) [cryptic](https://github.com/facebook/react/issues/6895) [errors](https://github.com/facebook/react/issues/8579) on next renders. These errors were always caused by an earlier error in the application code, but React did not provide a way to handle them gracefully in components, and could not recover from them.
+
+
+## Introducing Error Boundaries
+
+A JavaScript error in a part of the UI shouldn’t break the whole app. To solve this problem for React users, React 16 introduces a new concept of an “error boundary”.
+
+Error boundaries are React components that **catch JavaScript errors anywhere in their child component tree, log those errors, and display a fallback UI** instead of the component tree that crashed. Error boundaries catch errors during rendering, in lifecycle methods, and in constructors of the whole tree below them.
+
+A class component becomes an error boundary if it defines a new lifecycle method called `componentDidCatch(error, info)`:
+
+```js{7-12,15-18}
+class ErrorBoundary extends React.Component {
+  constructor(props) {
+    super(props);
+    this.state = { hasError: false };
+  }
+
+  componentDidCatch(error, info) {
+    // Display fallback UI
+    this.setState({ hasError: true });
+    // You can also log the error to an error reporting service
+    logErrorToMyService(error, info);
+  }
+
+  render() {
+    if (this.state.hasError) {
+      // You can render any custom fallback UI
+      return <h1>Something went wrong.</h1>;
+    }
+    return this.props.children;
+  }
+}
+```
+
+Then you can use it as a regular component:
+
+```js
+<ErrorBoundary>
+  <MyWidget />
+</ErrorBoundary>
+```
+
+The `componentDidCatch()` method works like a JavaScript `catch {}` block, but for components. Only class components can be error boundaries. In practice, most of the time you’ll want to declare an error boundary component once and use it throughout your application.
+
+Note that **error boundaries only catch errors in the components below them in the tree**. An error boundary can’t catch an error within itself. If an error boundary fails trying to render the error message, the error will propagate to the closest error boundary above it. This, too, is similar to how catch {} block works in JavaScript.
+
+### componentDidCatch Parameters
+
+`error` is an error that has been thrown.
+
+`info` is an object with `componentStack` key. The property has information about component stack during thrown error.
+
+```js
+//...
+componentDidCatch(error, info) {
+  
+  /* Example stack information:
+     in ComponentThatThrows (created by App)
+     in ErrorBoundary (created by App)
+     in div (created by App)
+     in App
+  */
+  logComponentStackToMyService(info.componentStack);
+}
+
+//...
+```
+
+## Live Demo
+
+Check out [this example of declaring and using an error boundary](https://codepen.io/gaearon/pen/wqvxGa?editors=0010) with [React 16 beta](https://github.com/facebook/react/issues/10294).
+
+
+## Where to Place Error Boundaries
+
+The granularity of error boundaries is up to you. You may wrap top-level route components to display a “Something went wrong” message to the user, just like server-side frameworks often handle crashes. You may also wrap individual widgets in an error boundary to protect them from crashing the rest of the application.
+
+
+## New Behavior for Uncaught Errors
+
+This change has an important implication. **As of React 16, errors that were not caught by any error boundary will result in unmounting of the whole React component tree.**
+
+We debated this decision, but in our experience it is worse to leave corrupted UI in place than to completely remove it. For example, in a product like Messenger leaving the broken UI visible could lead to somebody sending a message to the wrong person. Similarly, it is worse for a payments app to display a wrong amount than to render nothing.
+
+This change means that as you migrate to React 16, you will likely uncover existing crashes in your application that have been unnoticed before. Adding error boundaries lets you provide better user experience when something goes wrong.
+
+For example, Facebook Messenger wraps content of the sidebar, the info panel, the conversation log, and the message input into separate error boundaries. If some component in one of these UI areas crashes, the rest of them remain interactive.
+
+We also encourage you to use JS error reporting services (or build your own) so that you can learn about unhandled exceptions as they happen in production, and fix them.
+
+
+## Component Stack Traces
+
+React 16 prints all errors that occurred during rendering to the console in development, even if the application accidentally swallows them. In addition to the error message and the JavaScript stack, it also provides component stack traces. Now you can see where exactly in the component tree the failure has happened:
+
+<img src="../images/docs/error-boundaries-stack-trace.png" style="max-width:100%" alt="Error caught by Error Boundary component">
+
+You can also see the filenames and line numbers in the component stack trace. This works by default in [Create React App](https://github.com/facebookincubator/create-react-app) projects:
+
+<img src="../images/docs/error-boundaries-stack-trace-line-numbers.png" style="max-width:100%" alt="Error caught by Error Boundary component with line numbers">
+
+If you don’t use Create React App, you can add [this plugin](https://www.npmjs.com/package/babel-plugin-transform-react-jsx-source) manually to your Babel configuration. Note that it’s intended only for development and **must be disabled in production**.
+
+
+## Why Not Use try/catch?
+
+`try` / `catch` is great but it only works for imperative code:
+
+```js
+try {
+  showButton();
+} catch (error) {
+  // ...
+}
+```
+
+However, React components are declarative and specify *what* should be rendered:
+
+```js
+<Button />
+```
+
+Error boundaries preserve the declarative nature of React, and behave as you would expect. For example, even if an error occurs in a `componentDidUpdate` hook caused by a `setState` somewhere deep in the tree, it will still correctly propagate to the closest error boundary.
+
+
+## Naming Changes from React 15
+
+React 15 included a very limited support for error boundaries under a different method name: `unstable_handleError`. This method no longer works, and you will need to change it to `componentDidCatch` in your code starting from the first 16 beta release.
+
+For this change, we’ve provided a [codemod](https://github.com/reactjs/react-codemod#error-boundaries) to automatically migrate your code.

content/docs/codebase-overview.md

@@ -264,6 +264,21 @@ this.setState(partialState);
 
 Also, since `setState()` automatically [merges a partial state into the current state](/docs/state-and-lifecycle.html#state-updates-are-merged), we only needed to call it with the changed parts.
 
+## Controlled Input Null Value
+
+Specifying the value prop on a [controlled component](/docs/forms.html#controlled-components) prevents the user from changing the input unless you desire so. If you've specified a `value` but the input is still editable, you may have accidentally set `value` to `undefined` or `null`.
+
+The following code demonstrates this. (The input is locked at first but becomes editable after a short delay.)
+
+```javascript
+ReactDOM.render(<input value="hi" />, mountNode);
+
+setTimeout(function() {
+  ReactDOM.render(<input value={null} />, mountNode);
+}, 1000);
+
+```
+
 ## Alternatives to Controlled Components
 
 It can sometimes be tedious to use controlled components, because you need to write an event handler for every way your data can change and pipe all of the input state through a React component. This can become particularly annoying when you are converting a preexisting codebase to React, or integrating a React application with a non-React library. In these situations, you might want to check out [uncontrolled components](/docs/uncontrolled-components.html), an alternative technique for implementing input forms.

content/docs/error-boundaries.md

@@ -30,8 +30,8 @@ For example, say you have a `CommentList` component that subscribes to an extern
 
 ```js
 class CommentList extends React.Component {
-  constructor() {
-    super();
+  constructor(props) {
+    super(props);
     this.handleChange = this.handleChange.bind(this);
     this.state = {
       // "DataSource" is some global data source

content/docs/forms.md

@@ -24,13 +24,13 @@ Here are a couple of ways to get started:
 
 If you're just interested in playing around with React, you can use CodePen. Try starting from [this Hello World example code](http://codepen.io/gaearon/pen/rrpgNB?editors=0010). You don't need to install anything; you can just modify the code and see if it works.
 
-If you prefer to use your own text editor, you can also <a href="https://raw.githubusercontent.com/facebook/react/master/docs/downloads/single-file-example.html" download="hello.html">download this HTML file</a>, edit it, and open it from the local filesystem in your browser. It does a slow runtime code transformation, so don't use it in production.
+If you prefer to use your own text editor, you can also <a href="https://raw.githubusercontent.com/reactjs/reactjs.org/master/static/html/single-file-example.html" download="hello.html">download this HTML file</a>, edit it, and open it from the local filesystem in your browser. It does a slow runtime code transformation, so don't use it in production.
 
 If you want to use it for a full application, there are two popular ways to get started with React: using Create React App, or adding it to an existing application.
 
 ## Creating a New Application
 
-[Create React App](http://github.com/facebookincubator/create-react-app) is the best way to start building a new React single page application. It sets up your development environment so that you can use the latest JavaScript features, provides a nice developer experience, and optimizes your app for production.
+[Create React App](http://github.com/facebookincubator/create-react-app) is the best way to start building a new React single page application. It sets up your development environment so that you can use the latest JavaScript features, provides a nice developer experience, and optimizes your app for production. You’ll need to have Node >= 6 on your machine.
 
 ```bash
 npm install -g create-react-app
@@ -84,7 +84,7 @@ Both Yarn and npm download packages from the [npm registry](http://npmjs.com/).
 
 We recommend using React with [Babel](http://babeljs.io/) to let you use ES6 and JSX in your JavaScript code. ES6 is a set of modern JavaScript features that make development easier, and JSX is an extension to the JavaScript language that works nicely with React.
 
-The [Babel setup instructions](https://babeljs.io/docs/setup/) explain how to configure Babel in many different build environments. Make sure you install [`babel-preset-react`](http://babeljs.io/docs/plugins/preset-react/#basic-setup-with-the-cli-) and [`babel-preset-es2015`](http://babeljs.io/docs/plugins/preset-es2015/#basic-setup-with-the-cli-) and enable them in your [`.babelrc` configuration](http://babeljs.io/docs/usage/babelrc/), and you're good to go.
+The [Babel setup instructions](https://babeljs.io/docs/setup/) explain how to configure Babel in many different build environments. Make sure you install [`babel-preset-react`](http://babeljs.io/docs/plugins/preset-react/#basic-setup-with-the-cli-) and [`babel-preset-env`](http://babeljs.io/docs/plugins/preset-env/) and enable them in your [`.babelrc` configuration](http://babeljs.io/docs/usage/babelrc/), and you're good to go.
 
 ### Hello World with ES6 and JSX
 

content/docs/higher-order-components.md

@@ -48,6 +48,8 @@
       title: Context
     - id: portals
       title: Portals
+    - id: error-boundaries
+      title: Error Boundaries
     - id: web-components
       title: Web Components
     - id: higher-order-components

content/docs/installation.md

@@ -216,7 +216,7 @@ componentWillUpdate(nextProps, nextState)
 
 `componentWillUpdate()` is invoked immediately before rendering when new props or state are being received. Use this as an opportunity to perform preparation before an update occurs. This method is not called for the initial render.
 
-Note that you cannot call `this.setState()` here. If you need to update state in response to a prop change, use `componentWillReceiveProps()` instead.
+Note that you cannot call `this.setState()` here; nor should you do anything else (eg dispatch a redux action) that would trigger an update to a React component before `componentWillUpdate` returns. Use `componentWillReceiveProps()` if you need to update `state` in response to `props` changes.
 
 > Note
 >