Sync with reactjs.org @ d0f2db96

content/community/conferences.md

@@ -52,10 +52,10 @@ June 21, 2019 Chicago, Illinois USA
 
 [Website](https://reactloop.com) - [Twitter](https://twitter.com/ReactLoop)
 
-### React Week '19 {#RWNY19}
-July 15-21, 2019. New York City, USA
+### React Rally 2019
+August 22-23, 2019. Salt Lake City, USA.
 
-[Website](https://reactweek.nyc) - [Twitter](https://twitter.com/ReactWeek)
+[Website](https://www.reactrally.com/) - [Twitter](https://twitter.com/ReactRally) - [Instagram](https://www.instagram.com/reactrally/)
 
 ### ComponentsConf 2019 {#componentsconf-2019}
 September 6, 2019 in Melbourne, Australia

content/community/meetups.md

@@ -88,6 +88,7 @@ Do you have a local React.js meetup? Add it here! (Please keep the list alphabet
 
 ## Pakistan {#pakistan}
 * [Karachi](https://www.facebook.com/groups/902678696597634/)
+* [Lahore](https://www.facebook.com/groups/ReactjsLahore/)
 
 ## Peru {#peru}
 * [Lima](https://www.meetup.com/ReactJS-Peru/)
@@ -130,8 +131,8 @@ Do you have a local React.js meetup? Add it here! (Please keep the list alphabet
 * [New York, NY - ReactJS](https://www.meetup.com/NYC-Javascript-React-Group/)
 * [New York, NY - React Ladies](https://www.meetup.com/React-Ladies/)
 * [New York, NY - React Native](https://www.meetup.com/React-Native-NYC/)
-* [New York, NY - ReactNYC](https://www.meetup.com/ReactNYC/)
 * [Palo Alto, CA - React Native](https://www.meetup.com/React-Native-Silicon-Valley/)
+* [Philadelphia, PA - ReactJS](https://www.meetup.com/RQ-React/)
 * [Phoenix, AZ - ReactJS](https://www.meetup.com/ReactJS-Phoenix/)
 * [Pittsburgh, PA - ReactJS/React Native](https://www.meetup.com/ReactPgh/)
 * [Portland, OR - ReactJS](https://www.meetup.com/Portland-ReactJS/)

content/docs/hooks-faq.md

@@ -18,6 +18,7 @@ prev: hooks-reference.html
   ).join('\n')
 -->
 
+<<<<<<< HEAD
 * [Внедрение хуков](#adoption-strategy)
   * [В какой версии React появились хуки?](#which-versions-of-react-include-hooks)
   * [Нужно ли переписать все мои классовые компоненты?](#do-i-need-to-rewrite-all-my-class-components)
@@ -61,6 +62,52 @@ prev: hooks-reference.html
 ### В какой версии React появились хуки? {#which-versions-of-react-include-hooks}
 
 Начиная с релиза 16.8.0, React включает в себя стабильную реализацию хуков для:
+=======
+* **[Adoption Strategy](#adoption-strategy)**
+  * [Which versions of React include Hooks?](#which-versions-of-react-include-hooks)
+  * [Do I need to rewrite all my class components?](#do-i-need-to-rewrite-all-my-class-components)
+  * [What can I do with Hooks that I couldn't with classes?](#what-can-i-do-with-hooks-that-i-couldnt-with-classes)
+  * [How much of my React knowledge stays relevant?](#how-much-of-my-react-knowledge-stays-relevant)
+  * [Should I use Hooks, classes, or a mix of both?](#should-i-use-hooks-classes-or-a-mix-of-both)
+  * [Do Hooks cover all use cases for classes?](#do-hooks-cover-all-use-cases-for-classes)
+  * [Do Hooks replace render props and higher-order components?](#do-hooks-replace-render-props-and-higher-order-components)
+  * [What do Hooks mean for popular APIs like Redux connect() and React Router?](#what-do-hooks-mean-for-popular-apis-like-redux-connect-and-react-router)
+  * [Do Hooks work with static typing?](#do-hooks-work-with-static-typing)
+  * [How to test components that use Hooks?](#how-to-test-components-that-use-hooks)
+  * [What exactly do the lint rules enforce?](#what-exactly-do-the-lint-rules-enforce)
+* **[From Classes to Hooks](#from-classes-to-hooks)**
+  * [How do lifecycle methods correspond to Hooks?](#how-do-lifecycle-methods-correspond-to-hooks)
+  * [How can I do data fetching with Hooks?](#how-can-i-do-data-fetching-with-hooks)
+  * [Is there something like instance variables?](#is-there-something-like-instance-variables)
+  * [Should I use one or many state variables?](#should-i-use-one-or-many-state-variables)
+  * [Can I run an effect only on updates?](#can-i-run-an-effect-only-on-updates)
+  * [How to get the previous props or state?](#how-to-get-the-previous-props-or-state)
+  * [Why am I seeing stale props or state inside my function?](#why-am-i-seeing-stale-props-or-state-inside-my-function)
+  * [How do I implement getDerivedStateFromProps?](#how-do-i-implement-getderivedstatefromprops)
+  * [Is there something like forceUpdate?](#is-there-something-like-forceupdate)
+  * [Can I make a ref to a function component?](#can-i-make-a-ref-to-a-function-component)
+  * [How can I measure a DOM node?](#how-can-i-measure-a-dom-node)
+  * [What does const [thing, setThing] = useState() mean?](#what-does-const-thing-setthing--usestate-mean)
+* **[Performance Optimizations](#performance-optimizations)**
+  * [Can I skip an effect on updates?](#can-i-skip-an-effect-on-updates)
+  * [Is it safe to omit functions from the list of dependencies?](#is-it-safe-to-omit-functions-from-the-list-of-dependencies)
+  * [What can I do if my effect dependencies change too often?](#what-can-i-do-if-my-effect-dependencies-change-too-often)
+  * [How do I implement shouldComponentUpdate?](#how-do-i-implement-shouldcomponentupdate)
+  * [How to memoize calculations?](#how-to-memoize-calculations)
+  * [How to create expensive objects lazily?](#how-to-create-expensive-objects-lazily)
+  * [Are Hooks slow because of creating functions in render?](#are-hooks-slow-because-of-creating-functions-in-render)
+  * [How to avoid passing callbacks down?](#how-to-avoid-passing-callbacks-down)
+  * [How to read an often-changing value from useCallback?](#how-to-read-an-often-changing-value-from-usecallback)
+* **[Under the Hood](#under-the-hood)**
+  * [How does React associate Hook calls with components?](#how-does-react-associate-hook-calls-with-components)
+  * [What is the prior art for Hooks?](#what-is-the-prior-art-for-hooks)
+
+## Adoption Strategy {#adoption-strategy}
+
+### Which versions of React include Hooks? {#which-versions-of-react-include-hooks}
+
+Starting with 16.8.0, React includes a stable implementation of React Hooks for:
+>>>>>>> d0f2db967a38e358bd59c65e981862cdf38f3d0b
 
 * React DOM
 * React DOM Server
@@ -454,7 +501,65 @@ function ScrollView({row}) {
 
 Несмотря на то, что вам не понадобится это часто, вы можете предоставить некоторые императивные методы родительскому компоненту, используя хук [`useImperativeHandle`](/docs/hooks-reference.html#useimperativehandle).
 
+<<<<<<< HEAD
 ### Что значит `const [thing, setThing] = useState()`? {#what-does-const-thing-setthing--usestate-mean}
+=======
+### How can I measure a DOM node? {#how-can-i-measure-a-dom-node}
+
+In order to measure the position or size of a DOM node, you can use a [callback ref](/docs/refs-and-the-dom.html#callback-refs). React will call that callback whenever the ref gets attached to a different node. Here is a [small demo](https://codesandbox.io/s/l7m0v5x4v9):
+
+```js{4-8,12}
+function MeasureExample() {
+  const [height, setHeight] = useState(0);
+
+  const measuredRef = useCallback(node => {
+    if (node !== null) {
+      setHeight(node.getBoundingClientRect().height);
+    }
+  }, []);
+
+  return (
+    <>
+      <h1 ref={measuredRef}>Hello, world</h1>
+      <h2>The above header is {Math.round(height)}px tall</h2>
+    </>
+  );
+}
+```
+
+We didn't choose `useRef` in this example because an object ref doesn't notify us about *changes* to the current ref value. Using a callback ref ensures that [even if a child component displays the measured node later](https://codesandbox.io/s/818zzk8m78) (e.g. in response to a click), we still get notified about it in the parent component and can update the measurements.
+
+Note that we pass `[]` as a dependency array to `useCallback`. This ensures that our ref callback doesn't change between the re-renders, and so React won't call it unnecessarily.
+
+If you want, you can [extract this logic](https://codesandbox.io/s/m5o42082xy) into a reusable Hook:
+
+```js{2}
+function MeasureExample() {
+  const [rect, ref] = useClientRect();
+  return (
+    <>
+      <h1 ref={ref}>Hello, world</h1>
+      {rect !== null &&
+        <h2>The above header is {Math.round(rect.height)}px tall</h2>
+      }
+    </>
+  );
+}
+
+function useClientRect() {
+  const [rect, setRect] = useState(null);
+  const ref = useCallback(node => {
+    if (node !== null) {
+      setRect(node.getBoundingClientRect());
+    }
+  }, []);
+  return [rect, ref];
+}
+```
+
+
+### What does `const [thing, setThing] = useState()` mean? {#what-does-const-thing-setthing--usestate-mean}
+>>>>>>> d0f2db967a38e358bd59c65e981862cdf38f3d0b
 
 Если вы не знакомы с этим синтаксисом, ознакомьтесь с [объяснением](/docs/hooks-state.html#tip-what-do-square-brackets-mean) в документации хука состояния.
 
@@ -857,8 +962,13 @@ function Form() {
   const [text, updateText] = useState('');
   const textRef = useRef();
 
+<<<<<<< HEAD
   useLayoutEffect(() => {
     textRef.current = text; // Записать в реф
+=======
+  useEffect(() => {
+    textRef.current = text; // Write it to the ref
+>>>>>>> d0f2db967a38e358bd59c65e981862cdf38f3d0b
   });
 
   const handleSubmit = useCallback(() => {
@@ -898,7 +1008,7 @@ function useEventCallback(fn, dependencies) {
     throw new Error('Невозможно вызвать обработчик события во время рендера.');
   });
 
-  useLayoutEffect(() => {
+  useEffect(() => {
     ref.current = fn;
   }, [fn, ...dependencies]);
 

content/docs/hooks-reference.md

@@ -96,6 +96,8 @@ const [state, setState] = useState(() => {
 
 Если вы обновите состояние хука тем же значением, что и текущее состояние, React досрочно выйдет из хука без повторного рендера дочерних элементов и запуска эффектов. (React использует [алгоритм сравнения `Object.is`](https://developer.mozilla.org/ru/docs/Web/JavaScript/Reference/Global_Objects/Object/is#Description).)
 
+Note that React may still need to render that specific component again before bailing out. That shouldn't be a concern because React won't unnecessarily go "deeper" into the tree. If you're doing expensive calculations while rendering, you can optimize them with `useMemo`.
+
 ### `useEffect` {#useeffect}
 
 ```js
@@ -171,12 +173,32 @@ useEffect(
 ### `useContext` {#usecontext}
 
 ```js
-const context = useContext(Context);
+const value = useContext(MyContext);
 ```
 
+<<<<<<< HEAD
 Принимает объект контекста (значение, возвращённое из `React.createContext`) и возвращает текущее значение контекста, как указано ближайшим поставщиком контекста для данного контекста.
 
 Когда провайдер обновляется, этот хук инициирует повторный рендер с последним значением контекста.
+=======
+Accepts a context object (the value returned from `React.createContext`) and returns the current context value for that context. The current context value is determined by the `value` prop of the nearest `<MyContext.Provider>` above the calling component in the tree.
+
+When the nearest `<MyContext.Provider>` above the component updates, this Hook will trigger a rerender with the latest context `value` passed to that `MyContext` provider.
+
+Don't forget that the argument to `useContext` must be the *context object itself*:
+
+ * **Correct:** `useContext(MyContext)`
+ * **Incorrect:** `useContext(MyContext.Consumer)`
+ * **Incorrect:** `useContext(MyContext.Provider)`
+
+A component calling `useContext` will always re-render when the context value changes. If re-rendering the component is expensive, you can [optimize it by using memoization](https://github.com/facebook/react/issues/15156#issuecomment-474590693).
+
+>Tip
+>
+>If you're familiar with the context API before Hooks, `useContext(MyContext)` is equivalent to `static contextType = MyContext` in a class, or to `<MyContext.Consumer>`.
+>
+>`useContext(MyContext)` only lets you *read* the context and subscribe to its changes. You still need a `<MyContext.Provider>` above in the tree to *provide* the value for this context.
+>>>>>>> d0f2db967a38e358bd59c65e981862cdf38f3d0b
 
 ## Дополнительные хуки {#additional-hooks}
 
@@ -283,6 +305,8 @@ function Counter({initialCount}) {
 
 Если вы вернёте то же значение из редюсера хука, что и текущее состояние, React выйдет без перерисовки дочерних элементов или запуска эффектов. (React использует [алгоритм сравнения Object.is](https://developer.mozilla.org/ru/docs/Web/JavaScript/Reference/Global_Objects/Object/is#Description).)
 
+Note that React may still need to render that specific component again before bailing out. That shouldn't be a concern because React won't unnecessarily go "deeper" into the tree. If you're doing expensive calculations while rendering, you can optimize them with `useMemo`.
+
 ### `useCallback` {#usecallback}
 
 ```js
@@ -354,7 +378,20 @@ function TextInputWithFocusButton() {
 }
 ```
 
+<<<<<<< HEAD
 Обратите внимание, что `useRef()` полезен не только для атрибута `ref`. Он также [удобен для хранения любого изменяемого значения](/docs/hooks-faq.html#is-there-something-like-instance-variables) примерно так же, как вы используете поля экземпляров в классах.
+=======
+Essentially, `useRef` is like a "box" that can hold a mutable value in its `.current` property.
+
+You might be familiar with refs primarily as a way to [access the DOM](/docs/refs-and-the-dom.html). If you pass a ref object to React with `<div ref={myRef} />`, React will set its `.current` property to the corresponding DOM node whenever that node changes.
+
+However, `useRef()` is useful for more than the `ref` attribute. It's [handy for keeping any mutable value around](/docs/hooks-faq.html#is-there-something-like-instance-variables) similar to how you'd use instance fields in classes.
+
+This works because `useRef()` creates a plain JavaScript object. The only difference between `useRef()` and creating a `{current: ...}` object yourself is that `useRef` will give you the same ref object on every render.
+
+Keep in mind that `useRef` *doesn't* notify you when its content changes. Mutating the `.current` property doesn't cause a re-render. If you want to run some code when React attaches or detaches a ref to a DOM node, you may want to use a [callback ref](/docs/hooks-faq.html#how-can-i-measure-a-dom-node) instead.
+
+>>>>>>> d0f2db967a38e358bd59c65e981862cdf38f3d0b
 
 ### `useImperativeHandle` {#useimperativehandle}
 
@@ -387,7 +424,15 @@ FancyInput = forwardRef(FancyInput);
 
 > Совет
 >
+<<<<<<< HEAD
 > Если вы переносите код из классового компонента, `useLayoutEffect` запускается в той же фазе, что и `componentDidMount` и `componentDidUpdate`, поэтому, если вы не уверены, какой хук эффект использовать, это, вероятно, наименее рискованно.
+=======
+> If you're migrating code from a class component, note `useLayoutEffect` fires in the same phase as `componentDidMount` and `componentDidUpdate`. However, **we recommend starting with `useEffect` first** and only trying `useLayoutEffect` if that causes a problem.
+>
+>If you use server rendering, keep in mind that *neither* `useLayoutEffect` nor `useEffect` can run until the JavaScript is downloaded. This is why React warns when a server-rendered component contains `useLayoutEffect`. To fix this, either move that logic to `useEffect` (if it isn't necessary for the first render), or delay showing that component until after the client renders (if the HTML looks broken until `useLayoutEffect` runs).
+>
+>To exclude a component that needs layout effects from the server-rendered HTML, render it conditionally with `showChild && <Child />` and defer showing it with `useEffect(() => { setShowChild(true); }, [])`. This way, the UI doesn't appear broken before hydration.
+>>>>>>> d0f2db967a38e358bd59c65e981862cdf38f3d0b
 
 ### `useDebugValue` {#usedebugvalue}
 

content/docs/optimizing-performance.md

@@ -430,6 +430,10 @@ x === z; // true
 
 В этом случае, поскольку после мутирования `x` возвращается новая ссылка, мы можем использовать строгое сравнение (в данном случае по ссылке) `(x === y)` для того, чтобы убедиться, что новое значение хранящееся в `y` отличается от исходного значения, хранящегося в `x`.
 
+<<<<<<< HEAD
 Есть две другие библиотеки, которые могут помочь вам использовать иммутабельные данные: [seamless-immutable](https://github.com/rtfeldman/seamless-immutable) и [immutability-helper](https://github.com/kolodny/immutability-helper).
+=======
+Other libraries that can help use immutable data include [Immer](https://github.com/mweststrate/immer), [immutability-helper](https://github.com/kolodny/immutability-helper), and [seamless-immutable](https://github.com/rtfeldman/seamless-immutable).
+>>>>>>> d0f2db967a38e358bd59c65e981862cdf38f3d0b
 
 Иммутабельные структуры данных предоставляют вам дешёвый способ отслеживания изменений в объектах и всё, что вам нужно для реализации `shouldComponentUpdate`. В большинстве случаев это даст вам хороший прирост в производительности.

content/docs/reference-glossary.md

@@ -131,7 +131,11 @@ class Welcome extends React.Component {
 Методы жизненного цикла — это настраиваемые функции, которые выполняются на различных этапах жизни компонента. Существуют специальные методы для первоначального рендеринга компонента в DOM ([монтирование](/docs/react-component.html#mounting)), его обновления, размонтирования и удаления.
 
 
+<<<<<<< HEAD
  ## [Управляемые](/docs/forms.html#controlled-components) и [неуправляемые компоненты](/docs/uncontrolled-components.html)
+=======
+The most important difference between `state` and `props` is that `props` are passed from a parent component, but `state` is managed by the component itself. A component cannot change its `props`, but it can change its `state`.
+>>>>>>> d0f2db967a38e358bd59c65e981862cdf38f3d0b
 
 В React существует два различных подхода для управления формами.