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.../learn/state-a-components-memory.md | 979 +-----------------
1 file changed, 53 insertions(+), 926 deletions(-)
diff --git a/src/content/learn/state-a-components-memory.md b/src/content/learn/state-a-components-memory.md
index 73d46bdab8..275de11ba6 100644
--- a/src/content/learn/state-a-components-memory.md
+++ b/src/content/learn/state-a-components-memory.md
@@ -1,25 +1,25 @@
---
-title: "State: A Component's Memory"
+title: "Состояние: память компонента"
---
-
+```html
-Components often need to change what's on the screen as a result of an interaction. Typing into the form should update the input field, clicking "next" on an image carousel should change which image is displayed, clicking "buy" should put a product in the shopping cart. Components need to "remember" things: the current input value, the current image, the shopping cart. In React, this kind of component-specific memory is called *state*.
+Компоненты часто должны менять то, что отображается на экране, в результате взаимодействия. Ввод текста в форму должен обновлять поле ввода, нажатие «далее» в карусели изображений должно менять отображаемое изображение, нажатие «купить» должно помещать продукт в корзину. Компоненты должны «запоминать» вещи: текущее значение ввода, текущее изображение, корзину покупок. В React этот вид памяти, специфичный для компонента, называется *состоянием*.
-* How to add a state variable with the [`useState`](/reference/react/useState) Hook
-* What pair of values the `useState` Hook returns
-* How to add more than one state variable
-* Why state is called local
+* Как добавить переменную состояния с помощью хука [`useState`](/reference/react/useState)
+* Какую пару значений возвращает хук `useState`
+* Как добавить больше одной переменной состояния
+* Почему состояние называется локальным
-## When a regular variable isn’t enough {/*when-a-regular-variable-isnt-enough*/}
+## Когда обычной переменной недостаточно {/*when-a-regular-variable-isnt-enough*/}
-Here's a component that renders a sculpture image. Clicking the "Next" button should show the next sculpture by changing the `index` to `1`, then `2`, and so on. However, this **won't work** (you can try it!):
+Вот компонент, который отображает изображение скульптуры. Нажатие кнопки «Далее» должно показывать следующую скульптуру, изменяя `index` на `1`, затем `2` и так далее. Однако это **не сработает** (вы можете попробовать!).
@@ -151,46 +151,46 @@ button {
-The `handleClick` event handler is updating a local variable, `index`. But two things prevent that change from being visible:
+Обработчик события `handleClick` обновляет локальную переменную `index`. Но две вещи не позволяют этому изменению быть видимым:
-1. **Local variables don't persist between renders.** When React renders this component a second time, it renders it from scratch—it doesn't consider any changes to the local variables.
-2. **Changes to local variables won't trigger renders.** React doesn't realize it needs to render the component again with the new data.
+1. **Локальные переменные не сохраняются между рендерами.** Когда React повторно отрисовывает этот компонент, он отрисовывает его с нуля — он не учитывает какие-либо изменения локальных переменных.
+2. **Изменения локальных переменных не вызывают рендеринга.** React не понимает, что ему нужно снова отрисовать компонент с новыми данными.
-To update a component with new data, two things need to happen:
+Чтобы обновить компонент с новыми данными, необходимо, чтобы произошло две вещи:
-1. **Retain** the data between renders.
-2. **Trigger** React to render the component with new data (re-rendering).
+1. **Сохранить** данные между рендерами.
+2. **Запустить** React для отрисовки компонента с новыми данными (повторный рендеринг).
-The [`useState`](/reference/react/useState) Hook provides those two things:
+Хук [`useState`](/reference/react/useState) предоставляет эти две вещи:
-1. A **state variable** to retain the data between renders.
-2. A **state setter function** to update the variable and trigger React to render the component again.
+1. **Переменную состояния** для сохранения данных между рендерами.
+2. **Функцию установки состояния** для обновления переменной и запуска React для повторной отрисовки компонента.
-## Adding a state variable {/*adding-a-state-variable*/}
+## Добавление переменной состояния {/*adding-a-state-variable*/}
-To add a state variable, import `useState` from React at the top of the file:
+Чтобы добавить переменную состояния, импортируйте `useState` из React вверху файла:
```js
import { useState } from 'react';
```
-Then, replace this line:
+Затем замените эту строку:
```js
let index = 0;
```
-with
+на
```js
const [index, setIndex] = useState(0);
```
-`index` is a state variable and `setIndex` is the setter function.
+`index` — это переменная состояния, а `setIndex` — функция установки состояния.
-> The `[` and `]` syntax here is called [array destructuring](https://javascript.info/destructuring-assignment) and it lets you read values from an array. The array returned by `useState` always has exactly two items.
+> Синтаксис `[` и `]` здесь называется [деструктуризацией массива](https://javascript.info/destructuring-assignment), и он позволяет вам считывать значения из массива. Массив, возвращаемый `useState`, всегда имеет ровно два элемента.
-This is how they work together in `handleClick`:
+Вот как они работают вместе в `handleClick`:
```js
function handleClick() {
@@ -198,7 +198,7 @@ function handleClick() {
}
```
-Now clicking the "Next" button switches the current sculpture:
+Теперь нажатие кнопки «Далее» переключает текущую скульптуру:
@@ -331,57 +331,57 @@ button {
-### Meet your first Hook {/*meet-your-first-hook*/}
+### Знакомьтесь, ваш первый хук {/*meet-your-first-hook*/}
-In React, `useState`, as well as any other function starting with "`use`", is called a Hook.
+В React `useState`, а также любая другая функция, начинающаяся с «`use`», называется хуком.
-*Hooks* are special functions that are only available while React is [rendering](/learn/render-and-commit#step-1-trigger-a-render) (which we'll get into in more detail on the next page). They let you "hook into" different React features.
+*Хуки* — это специальные функции, которые доступны только во время [рендеринга](/learn/render-and-commit#step-1-trigger-a-render) React (о чем мы подробно расскажем на следующей странице). Они позволяют вам «подключаться» к различным функциям React.
-State is just one of those features, but you will meet the other Hooks later.
+Состояние — это всего лишь одна из этих функций, но с другими хуками вы познакомитесь позже.
-**Hooks—functions starting with `use`—can only be called at the top level of your components or [your own Hooks.](/learn/reusing-logic-with-custom-hooks)** You can't call Hooks inside conditions, loops, or other nested functions. Hooks are functions, but it's helpful to think of them as unconditional declarations about your component's needs. You "use" React features at the top of your component similar to how you "import" modules at the top of your file.
+**Хуки — функции, начинающиеся с `use` — можно вызывать только на верхнем уровне ваших компонентов или [ваших собственных хуков.](/learn/reusing-logic-with-custom-hooks)** Вы не можете вызывать хуки внутри условий, циклов или других вложенных функций. Хуки — это функции, но полезно думать о них как о безусловных объявлениях о потребностях вашего компонента. Вы «используете» функции React в верхней части вашего компонента, аналогично тому, как вы «импортируете» модули в верхней части вашего файла.
-### Anatomy of `useState` {/*anatomy-of-usestate*/}
+### Анатомия `useState` {/*anatomy-of-usestate*/}
-When you call [`useState`](/reference/react/useState), you are telling React that you want this component to remember something:
+Когда вы вызываете [`useState`](/reference/react/useState), вы сообщаете React, что хотите, чтобы этот компонент что-то запомнил:
```js
const [index, setIndex] = useState(0);
```
-In this case, you want React to remember `index`.
+В этом случае вы хотите, чтобы React запомнил `index`.
-The convention is to name this pair like `const [something, setSomething]`. You could name it anything you like, but conventions make things easier to understand across projects.
+Принято называть эту пару как `const [something, setSomething]`. Вы можете назвать ее как угодно, но соглашения упрощают понимание в разных проектах.
-The only argument to `useState` is the **initial value** of your state variable. In this example, the `index`'s initial value is set to `0` with `useState(0)`.
+Единственным аргументом для `useState` является **начальное значение** вашей переменной состояния. В этом примере начальное значение `index` установлено в `0` с помощью `useState(0)`.
-Every time your component renders, `useState` gives you an array containing two values:
+Каждый раз, когда ваш компонент отрисовывается, `useState` предоставляет вам массив, содержащий два значения:
-1. The **state variable** (`index`) with the value you stored.
-2. The **state setter function** (`setIndex`) which can update the state variable and trigger React to render the component again.
+1. **Переменную состояния** (`index`) со значением, которое вы сохранили.
+2. **Функцию установки состояния** (`setIndex`), которая может обновить переменную состояния и запустить React для повторной отрисовки компонента.
-Here's how that happens in action:
+Вот как это происходит на практике:
```js
const [index, setIndex] = useState(0);
```
-1. **Your component renders the first time.** Because you passed `0` to `useState` as the initial value for `index`, it will return `[0, setIndex]`. React remembers `0` is the latest state value.
-2. **You update the state.** When a user clicks the button, it calls `setIndex(index + 1)`. `index` is `0`, so it's `setIndex(1)`. This tells React to remember `index` is `1` now and triggers another render.
-3. **Your component's second render.** React still sees `useState(0)`, but because React *remembers* that you set `index` to `1`, it returns `[1, setIndex]` instead.
-4. And so on!
+1. **Ваш компонент отрисовывается в первый раз.** Поскольку вы передали `0` в `useState` в качестве начального значения для `index`, он вернет `[0, setIndex]`. React помнит, что `0` — это последнее значение состояния.
+2. **Вы обновляете состояние.** Когда пользователь нажимает кнопку, она вызывает `setIndex(index + 1)`. `index` равен `0`, поэтому это `setIndex(1)`. Это сообщает React, что нужно запомнить, что `index` теперь равен `1`, и запускает другой рендеринг.
+3. **Второй рендеринг вашего компонента.** React по-прежнему видит `useState(0)`, но поскольку React *помнит*, что вы установили `index` равным `1`, он возвращает `[1, setIndex]` вместо этого.
+4. И так далее!
-## Giving a component multiple state variables {/*giving-a-component-multiple-state-variables*/}
+## Предоставление компоненту нескольких переменных состояния {/*giving-a-component-multiple-state-variables*/}
-You can have as many state variables of as many types as you like in one component. This component has two state variables, a number `index` and a boolean `showMore` that's toggled when you click "Show details":
+У вас может быть столько переменных состояния любого типа, сколько вам нравится, в одном компоненте. Этот компонент имеет две переменные состояния: число `index` и логическое значение `showMore`, которое переключается при нажатии «Показать подробности»:
@@ -520,19 +520,19 @@ button {
-It is a good idea to have multiple state variables if their state is unrelated, like `index` and `showMore` in this example. But if you find that you often change two state variables together, it might be easier to combine them into one. For example, if you have a form with many fields, it's more convenient to have a single state variable that holds an object than state variable per field. Read [Choosing the State Structure](/learn/choosing-the-state-structure) for more tips.
+Хорошей идеей является наличие нескольких переменных состояния, если их состояние не связано, как `index` и `showMore` в этом примере. Но если вы обнаружите, что часто изменяете две переменные состояния вместе, может быть проще объединить их в одну. Например, если у вас есть форма с множеством полей, удобнее иметь одну переменную состояния, которая содержит объект, чем переменную состояния для каждого поля. Прочтите [Выбор структуры состояния](/learn/choosing-the-state-structure) для получения дополнительных советов.
-#### How does React know which state to return? {/*how-does-react-know-which-state-to-return*/}
+#### Как React узнает, какое состояние возвращать? {/*how-does-react-know-which-state-to-return*/}
-You might have noticed that the `useState` call does not receive any information about *which* state variable it refers to. There is no "identifier" that is passed to `useState`, so how does it know which of the state variables to return? Does it rely on some magic like parsing your functions? The answer is no.
+Вы могли заметить, что вызов `useState` не получает никакой информации о *какой* переменной состояния он относится. Нет «идентификатора», который передается в `useState`, так как же он узнает, какую из переменных состояния вернуть? Полагается ли он на какую-то магию, например, на синтаксический анализ ваших функций? Ответ — нет.
-Instead, to enable their concise syntax, Hooks **rely on a stable call order on every render of the same component.** This works well in practice because if you follow the rule above ("only call Hooks at the top level"), Hooks will always be called in the same order. Additionally, a [linter plugin](https://www.npmjs.com/package/eslint-plugin-react-hooks) catches most mistakes.
+Вместо этого, чтобы включить их краткий синтаксис, хуки **основываются на стабильном порядке вызовов при каждом рендеринге одного и того же компонента.** Это хорошо работает на практике, потому что, если вы будете следовать правилу выше («вызывать хуки только на верхнем уровне»), хуки всегда будут вызываться в одном и том же порядке. Кроме того, [плагин линтера](https://www.npmjs.com/package/eslint-plugin-react-hooks) отлавливает большинство ошибок.
-Internally, React holds an array of state pairs for every component. It also maintains the current pair index, which is set to `0` before rendering. Each time you call `useState`, React gives you the next state pair and increments the index. You can read more about this mechanism in [React Hooks: Not Magic, Just Arrays.](https://medium.com/@ryardley/react-hooks-not-magic-just-arrays-cd4f1857236e)
+Внутри React хранит массив пар состояний для каждого компонента. Он также поддерживает текущий индекс пары, который устанавливается в `0` перед рендерингом. Каждый раз, когда вы вызываете `useState`, React предоставляет вам следующую пару состояний и увеличивает индекс. Вы можете прочитать больше об этом механизме в [React Hooks: Not Magic, Just Arrays.](https://medium.com/@ryardley/react-hooks-not-magic-just-arrays-cd4f1857236e)
-This example **doesn't use React** but it gives you an idea of how `useState` works internally:
+Этот пример **не использует React**, но он дает вам представление о том, как `useState` работает внутри:
@@ -635,877 +635,4 @@ let sculptureList = [{
artist: 'Eduardo Catalano',
description: 'This enormous (75 ft. or 23m) silver flower is located in Buenos Aires. It is designed to move, closing its petals in the evening or when strong winds blow and opening them in the morning.',
url: 'https://i.imgur.com/ZF6s192m.jpg',
- alt: 'A gigantic metallic flower sculpture with reflective mirror-like petals and strong stamens.'
-}, {
- name: 'Eternal Presence',
- artist: 'John Woodrow Wilson',
- description: 'Wilson was known for his preoccupation with equality, social justice, as well as the essential and spiritual qualities of humankind. This massive (7ft. or 2,13m) bronze represents what he described as "a symbolic Black presence infused with a sense of universal humanity."',
- url: 'https://i.imgur.com/aTtVpES.jpg',
- alt: 'The sculpture depicting a human head seems ever-present and solemn. It radiates calm and serenity.'
-}, {
- name: 'Moai',
- artist: 'Unknown Artist',
- description: 'Located on the Easter Island, there are 1,000 moai, or extant monumental statues, created by the early Rapa Nui people, which some believe represented deified ancestors.',
- url: 'https://i.imgur.com/RCwLEoQm.jpg',
- alt: 'Three monumental stone busts with the heads that are disproportionately large with somber faces.'
-}, {
- name: 'Blue Nana',
- artist: 'Niki de Saint Phalle',
- description: 'The Nanas are triumphant creatures, symbols of femininity and maternity. Initially, Saint Phalle used fabric and found objects for the Nanas, and later on introduced polyester to achieve a more vibrant effect.',
- url: 'https://i.imgur.com/Sd1AgUOm.jpg',
- alt: 'A large mosaic sculpture of a whimsical dancing female figure in a colorful costume emanating joy.'
-}, {
- name: 'Ultimate Form',
- artist: 'Barbara Hepworth',
- description: 'This abstract bronze sculpture is a part of The Family of Man series located at Yorkshire Sculpture Park. Hepworth chose not to create literal representations of the world but developed abstract forms inspired by people and landscapes.',
- url: 'https://i.imgur.com/2heNQDcm.jpg',
- alt: 'A tall sculpture made of three elements stacked on each other reminding of a human figure.'
-}, {
- name: 'Cavaliere',
- artist: 'Lamidi Olonade Fakeye',
- description: "Descended from four generations of woodcarvers, Fakeye's work blended traditional and contemporary Yoruba themes.",
- url: 'https://i.imgur.com/wIdGuZwm.png',
- alt: 'An intricate wood sculpture of a warrior with a focused face on a horse adorned with patterns.'
-}, {
- name: 'Big Bellies',
- artist: 'Alina Szapocznikow',
- description: "Szapocznikow is known for her sculptures of the fragmented body as a metaphor for the fragility and impermanence of youth and beauty. This sculpture depicts two very realistic large bellies stacked on top of each other, each around five feet (1,5m) tall.",
- url: 'https://i.imgur.com/AlHTAdDm.jpg',
- alt: 'The sculpture reminds a cascade of folds, quite different from bellies in classical sculptures.'
-}, {
- name: 'Terracotta Army',
- artist: 'Unknown Artist',
- description: 'The Terracotta Army is a collection of terracotta sculptures depicting the armies of Qin Shi Huang, the first Emperor of China. The army consisted of more than 8,000 soldiers, 130 chariots with 520 horses, and 150 cavalry horses.',
- url: 'https://i.imgur.com/HMFmH6m.jpg',
- alt: '12 terracotta sculptures of solemn warriors, each with a unique facial expression and armor.'
-}, {
- name: 'Lunar Landscape',
- artist: 'Louise Nevelson',
- description: 'Nevelson was known for scavenging objects from New York City debris, which she would later assemble into monumental constructions. In this one, she used disparate parts like a bedpost, juggling pin, and seat fragment, nailing and gluing them into boxes that reflect the influence of Cubism’s geometric abstraction of space and form.',
- url: 'https://i.imgur.com/rN7hY6om.jpg',
- alt: 'A black matte sculpture where the individual elements are initially indistinguishable.'
-}, {
- name: 'Aureole',
- artist: 'Ranjani Shettar',
- description: 'Shettar merges the traditional and the modern, the natural and the industrial. Her art focuses on the relationship between man and nature. Her work was described as compelling both abstractly and figuratively, gravity defying, and a "fine synthesis of unlikely materials."',
- url: 'https://i.imgur.com/okTpbHhm.jpg',
- alt: 'A pale wire-like sculpture mounted on concrete wall and descending on the floor. It appears light.'
-}, {
- name: 'Hippos',
- artist: 'Taipei Zoo',
- description: 'The Taipei Zoo commissioned a Hippo Square featuring submerged hippos at play.',
- url: 'https://i.imgur.com/6o5Vuyu.jpg',
- alt: 'A group of bronze hippo sculptures emerging from the sett sidewalk as if they were swimming.'
-}];
-
-// Make UI match the initial state.
-updateDOM();
-```
-
-```html public/index.html
-
-
-
-
-
-
-
-```
-
-```css
-button { display: block; margin-bottom: 10px; }
-```
-
-
-
-You don't have to understand it to use React, but you might find this a helpful mental model.
-
-
-
-## State is isolated and private {/*state-is-isolated-and-private*/}
-
-State is local to a component instance on the screen. In other words, **if you render the same component twice, each copy will have completely isolated state!** Changing one of them will not affect the other.
-
-In this example, the `Gallery` component from earlier is rendered twice with no changes to its logic. Try clicking the buttons inside each of the galleries. Notice that their state is independent:
-
-
-
-```js
-import Gallery from './Gallery.js';
-
-export default function Page() {
- return (
-
}
-
-
- );
-}
-```
-
-```js src/data.js
-export const sculptureList = [{
- name: 'Homenaje a la Neurocirugía',
- artist: 'Marta Colvin Andrade',
- description: 'Although Colvin is predominantly known for abstract themes that allude to pre-Hispanic symbols, this gigantic sculpture, an homage to neurosurgery, is one of her most recognizable public art pieces.',
- url: 'https://i.imgur.com/Mx7dA2Y.jpg',
- alt: 'A bronze statue of two crossed hands delicately holding a human brain in their fingertips.'
-}, {
- name: 'Floralis Genérica',
- artist: 'Eduardo Catalano',
- description: 'This enormous (75 ft. or 23m) silver flower is located in Buenos Aires. It is designed to move, closing its petals in the evening or when strong winds blow and opening them in the morning.',
- url: 'https://i.imgur.com/ZF6s192m.jpg',
- alt: 'A gigantic metallic flower sculpture with reflective mirror-like petals and strong stamens.'
-}, {
- name: 'Eternal Presence',
- artist: 'John Woodrow Wilson',
- description: 'Wilson was known for his preoccupation with equality, social justice, as well as the essential and spiritual qualities of humankind. This massive (7ft. or 2,13m) bronze represents what he described as "a symbolic Black presence infused with a sense of universal humanity."',
- url: 'https://i.imgur.com/aTtVpES.jpg',
- alt: 'The sculpture depicting a human head seems ever-present and solemn. It radiates calm and serenity.'
-}, {
- name: 'Moai',
- artist: 'Unknown Artist',
- description: 'Located on the Easter Island, there are 1,000 moai, or extant monumental statues, created by the early Rapa Nui people, which some believe represented deified ancestors.',
- url: 'https://i.imgur.com/RCwLEoQm.jpg',
- alt: 'Three monumental stone busts with the heads that are disproportionately large with somber faces.'
-}, {
- name: 'Blue Nana',
- artist: 'Niki de Saint Phalle',
- description: 'The Nanas are triumphant creatures, symbols of femininity and maternity. Initially, Saint Phalle used fabric and found objects for the Nanas, and later on introduced polyester to achieve a more vibrant effect.',
- url: 'https://i.imgur.com/Sd1AgUOm.jpg',
- alt: 'A large mosaic sculpture of a whimsical dancing female figure in a colorful costume emanating joy.'
-}, {
- name: 'Ultimate Form',
- artist: 'Barbara Hepworth',
- description: 'This abstract bronze sculpture is a part of The Family of Man series located at Yorkshire Sculpture Park. Hepworth chose not to create literal representations of the world but developed abstract forms inspired by people and landscapes.',
- url: 'https://i.imgur.com/2heNQDcm.jpg',
- alt: 'A tall sculpture made of three elements stacked on each other reminding of a human figure.'
-}, {
- name: 'Cavaliere',
- artist: 'Lamidi Olonade Fakeye',
- description: "Descended from four generations of woodcarvers, Fakeye's work blended traditional and contemporary Yoruba themes.",
- url: 'https://i.imgur.com/wIdGuZwm.png',
- alt: 'An intricate wood sculpture of a warrior with a focused face on a horse adorned with patterns.'
-}, {
- name: 'Big Bellies',
- artist: 'Alina Szapocznikow',
- description: "Szapocznikow is known for her sculptures of the fragmented body as a metaphor for the fragility and impermanence of youth and beauty. This sculpture depicts two very realistic large bellies stacked on top of each other, each around five feet (1,5m) tall.",
- url: 'https://i.imgur.com/AlHTAdDm.jpg',
- alt: 'The sculpture reminds a cascade of folds, quite different from bellies in classical sculptures.'
-}, {
- name: 'Terracotta Army',
- artist: 'Unknown Artist',
- description: 'The Terracotta Army is a collection of terracotta sculptures depicting the armies of Qin Shi Huang, the first Emperor of China. The army consisted of more than 8,000 soldiers, 130 chariots with 520 horses, and 150 cavalry horses.',
- url: 'https://i.imgur.com/HMFmH6m.jpg',
- alt: '12 terracotta sculptures of solemn warriors, each with a unique facial expression and armor.'
-}, {
- name: 'Lunar Landscape',
- artist: 'Louise Nevelson',
- description: 'Nevelson was known for scavenging objects from New York City debris, which she would later assemble into monumental constructions. In this one, she used disparate parts like a bedpost, juggling pin, and seat fragment, nailing and gluing them into boxes that reflect the influence of Cubism’s geometric abstraction of space and form.',
- url: 'https://i.imgur.com/rN7hY6om.jpg',
- alt: 'A black matte sculpture where the individual elements are initially indistinguishable.'
-}, {
- name: 'Aureole',
- artist: 'Ranjani Shettar',
- description: 'Shettar merges the traditional and the modern, the natural and the industrial. Her art focuses on the relationship between man and nature. Her work was described as compelling both abstractly and figuratively, gravity defying, and a "fine synthesis of unlikely materials."',
- url: 'https://i.imgur.com/okTpbHhm.jpg',
- alt: 'A pale wire-like sculpture mounted on concrete wall and descending on the floor. It appears light.'
-}, {
- name: 'Hippos',
- artist: 'Taipei Zoo',
- description: 'The Taipei Zoo commissioned a Hippo Square featuring submerged hippos at play.',
- url: 'https://i.imgur.com/6o5Vuyu.jpg',
- alt: 'A group of bronze hippo sculptures emerging from the sett sidewalk as if they were swimming.'
-}];
-```
-
-```css
-button { display: block; margin-bottom: 10px; }
-.Page > * {
- float: left;
- width: 50%;
- padding: 10px;
-}
-h2 { margin-top: 10px; margin-bottom: 0; }
-h3 {
- margin-top: 5px;
- font-weight: normal;
- font-size: 100%;
-}
-img { width: 120px; height: 120px; }
-button {
- display: block;
- margin-top: 10px;
- margin-bottom: 10px;
-}
-```
-
-
-
-This is what makes state different from regular variables that you might declare at the top of your module. State is not tied to a particular function call or a place in the code, but it's "local" to the specific place on the screen. You rendered two `` components, so their state is stored separately.
-
-Also notice how the `Page` component doesn't "know" anything about the `Gallery` state or even whether it has any. Unlike props, **state is fully private to the component declaring it.** The parent component can't change it. This lets you add state to any component or remove it without impacting the rest of the components.
-
-What if you wanted both galleries to keep their states in sync? The right way to do it in React is to *remove* state from child components and add it to their closest shared parent. The next few pages will focus on organizing state of a single component, but we will return to this topic in [Sharing State Between Components.](/learn/sharing-state-between-components)
-
-
-
-* Use a state variable when a component needs to "remember" some information between renders.
-* State variables are declared by calling the `useState` Hook.
-* Hooks are special functions that start with `use`. They let you "hook into" React features like state.
-* Hooks might remind you of imports: they need to be called unconditionally. Calling Hooks, including `useState`, is only valid at the top level of a component or another Hook.
-* The `useState` Hook returns a pair of values: the current state and the function to update it.
-* You can have more than one state variable. Internally, React matches them up by their order.
-* State is private to the component. If you render it in two places, each copy gets its own state.
-
-
-
-
-
-
-
-#### Complete the gallery {/*complete-the-gallery*/}
-
-When you press "Next" on the last sculpture, the code crashes. Fix the logic to prevent the crash. You may do this by adding extra logic to event handler or by disabling the button when the action is not possible.
-
-After fixing the crash, add a "Previous" button that shows the previous sculpture. It shouldn't crash on the first sculpture.
-
-
-
-```js
-import { useState } from 'react';
-import { sculptureList } from './data.js';
-
-export default function Gallery() {
- const [index, setIndex] = useState(0);
- const [showMore, setShowMore] = useState(false);
-
- function handleNextClick() {
- setIndex(index + 1);
- }
-
- function handleMoreClick() {
- setShowMore(!showMore);
- }
-
- let sculpture = sculptureList[index];
- return (
- <>
-
-
- {sculpture.name}
- by {sculpture.artist}
-
-
- ({index + 1} of {sculptureList.length})
-
-
- {showMore &&
{sculpture.description}
}
-
-
- );
-}
-```
-
-```js src/data.js
-export const sculptureList = [{
- name: 'Homenaje a la Neurocirugía',
- artist: 'Marta Colvin Andrade',
- description: 'Although Colvin is predominantly known for abstract themes that allude to pre-Hispanic symbols, this gigantic sculpture, an homage to neurosurgery, is one of her most recognizable public art pieces.',
- url: 'https://i.imgur.com/Mx7dA2Y.jpg',
- alt: 'A bronze statue of two crossed hands delicately holding a human brain in their fingertips.'
-}, {
- name: 'Floralis Genérica',
- artist: 'Eduardo Catalano',
- description: 'This enormous (75 ft. or 23m) silver flower is located in Buenos Aires. It is designed to move, closing its petals in the evening or when strong winds blow and opening them in the morning.',
- url: 'https://i.imgur.com/ZF6s192m.jpg',
- alt: 'A gigantic metallic flower sculpture with reflective mirror-like petals and strong stamens.'
-}, {
- name: 'Eternal Presence',
- artist: 'John Woodrow Wilson',
- description: 'Wilson was known for his preoccupation with equality, social justice, as well as the essential and spiritual qualities of humankind. This massive (7ft. or 2,13m) bronze represents what he described as "a symbolic Black presence infused with a sense of universal humanity."',
- url: 'https://i.imgur.com/aTtVpES.jpg',
- alt: 'The sculpture depicting a human head seems ever-present and solemn. It radiates calm and serenity.'
-}, {
- name: 'Moai',
- artist: 'Unknown Artist',
- description: 'Located on the Easter Island, there are 1,000 moai, or extant monumental statues, created by the early Rapa Nui people, which some believe represented deified ancestors.',
- url: 'https://i.imgur.com/RCwLEoQm.jpg',
- alt: 'Three monumental stone busts with the heads that are disproportionately large with somber faces.'
-}, {
- name: 'Blue Nana',
- artist: 'Niki de Saint Phalle',
- description: 'The Nanas are triumphant creatures, symbols of femininity and maternity. Initially, Saint Phalle used fabric and found objects for the Nanas, and later on introduced polyester to achieve a more vibrant effect.',
- url: 'https://i.imgur.com/Sd1AgUOm.jpg',
- alt: 'A large mosaic sculpture of a whimsical dancing female figure in a colorful costume emanating joy.'
-}, {
- name: 'Ultimate Form',
- artist: 'Barbara Hepworth',
- description: 'This abstract bronze sculpture is a part of The Family of Man series located at Yorkshire Sculpture Park. Hepworth chose not to create literal representations of the world but developed abstract forms inspired by people and landscapes.',
- url: 'https://i.imgur.com/2heNQDcm.jpg',
- alt: 'A tall sculpture made of three elements stacked on each other reminding of a human figure.'
-}, {
- name: 'Cavaliere',
- artist: 'Lamidi Olonade Fakeye',
- description: "Descended from four generations of woodcarvers, Fakeye's work blended traditional and contemporary Yoruba themes.",
- url: 'https://i.imgur.com/wIdGuZwm.png',
- alt: 'An intricate wood sculpture of a warrior with a focused face on a horse adorned with patterns.'
-}, {
- name: 'Big Bellies',
- artist: 'Alina Szapocznikow',
- description: "Szapocznikow is known for her sculptures of the fragmented body as a metaphor for the fragility and impermanence of youth and beauty. This sculpture depicts two very realistic large bellies stacked on top of each other, each around five feet (1,5m) tall.",
- url: 'https://i.imgur.com/AlHTAdDm.jpg',
- alt: 'The sculpture reminds a cascade of folds, quite different from bellies in classical sculptures.'
-}, {
- name: 'Terracotta Army',
- artist: 'Unknown Artist',
- description: 'The Terracotta Army is a collection of terracotta sculptures depicting the armies of Qin Shi Huang, the first Emperor of China. The army consisted of more than 8,000 soldiers, 130 chariots with 520 horses, and 150 cavalry horses.',
- url: 'https://i.imgur.com/HMFmH6m.jpg',
- alt: '12 terracotta sculptures of solemn warriors, each with a unique facial expression and armor.'
-}, {
- name: 'Lunar Landscape',
- artist: 'Louise Nevelson',
- description: 'Nevelson was known for scavenging objects from New York City debris, which she would later assemble into monumental constructions. In this one, she used disparate parts like a bedpost, juggling pin, and seat fragment, nailing and gluing them into boxes that reflect the influence of Cubism’s geometric abstraction of space and form.',
- url: 'https://i.imgur.com/rN7hY6om.jpg',
- alt: 'A black matte sculpture where the individual elements are initially indistinguishable.'
-}, {
- name: 'Aureole',
- artist: 'Ranjani Shettar',
- description: 'Shettar merges the traditional and the modern, the natural and the industrial. Her art focuses on the relationship between man and nature. Her work was described as compelling both abstractly and figuratively, gravity defying, and a "fine synthesis of unlikely materials."',
- url: 'https://i.imgur.com/okTpbHhm.jpg',
- alt: 'A pale wire-like sculpture mounted on concrete wall and descending on the floor. It appears light.'
-}, {
- name: 'Hippos',
- artist: 'Taipei Zoo',
- description: 'The Taipei Zoo commissioned a Hippo Square featuring submerged hippos at play.',
- url: 'https://i.imgur.com/6o5Vuyu.jpg',
- alt: 'A group of bronze hippo sculptures emerging from the sett sidewalk as if they were swimming.'
-}];
-```
-
-```css
-button { display: block; margin-bottom: 10px; }
-.Page > * {
- float: left;
- width: 50%;
- padding: 10px;
-}
-h2 { margin-top: 10px; margin-bottom: 0; }
-h3 {
- margin-top: 5px;
- font-weight: normal;
- font-size: 100%;
-}
-img { width: 120px; height: 120px; }
-```
-
-
-
-
-
-This adds a guarding condition inside both event handlers and disables the buttons when needed:
-
-
-
-```js
-import { useState } from 'react';
-import { sculptureList } from './data.js';
-
-export default function Gallery() {
- const [index, setIndex] = useState(0);
- const [showMore, setShowMore] = useState(false);
-
- let hasPrev = index > 0;
- let hasNext = index < sculptureList.length - 1;
-
- function handlePrevClick() {
- if (hasPrev) {
- setIndex(index - 1);
- }
- }
-
- function handleNextClick() {
- if (hasNext) {
- setIndex(index + 1);
- }
- }
-
- function handleMoreClick() {
- setShowMore(!showMore);
- }
-
- let sculpture = sculptureList[index];
- return (
- <>
-
-
-
- {sculpture.name}
- by {sculpture.artist}
-
-
- ({index + 1} of {sculptureList.length})
-
-
- {showMore &&
{sculpture.description}
}
-
-
- );
-}
-```
-
-```js src/data.js hidden
-export const sculptureList = [{
- name: 'Homenaje a la Neurocirugía',
- artist: 'Marta Colvin Andrade',
- description: 'Although Colvin is predominantly known for abstract themes that allude to pre-Hispanic symbols, this gigantic sculpture, an homage to neurosurgery, is one of her most recognizable public art pieces.',
- url: 'https://i.imgur.com/Mx7dA2Y.jpg',
- alt: 'A bronze statue of two crossed hands delicately holding a human brain in their fingertips.'
-}, {
- name: 'Floralis Genérica',
- artist: 'Eduardo Catalano',
- description: 'This enormous (75 ft. or 23m) silver flower is located in Buenos Aires. It is designed to move, closing its petals in the evening or when strong winds blow and opening them in the morning.',
- url: 'https://i.imgur.com/ZF6s192m.jpg',
- alt: 'A gigantic metallic flower sculpture with reflective mirror-like petals and strong stamens.'
-}, {
- name: 'Eternal Presence',
- artist: 'John Woodrow Wilson',
- description: 'Wilson was known for his preoccupation with equality, social justice, as well as the essential and spiritual qualities of humankind. This massive (7ft. or 2,13m) bronze represents what he described as "a symbolic Black presence infused with a sense of universal humanity."',
- url: 'https://i.imgur.com/aTtVpES.jpg',
- alt: 'The sculpture depicting a human head seems ever-present and solemn. It radiates calm and serenity.'
-}, {
- name: 'Moai',
- artist: 'Unknown Artist',
- description: 'Located on the Easter Island, there are 1,000 moai, or extant monumental statues, created by the early Rapa Nui people, which some believe represented deified ancestors.',
- url: 'https://i.imgur.com/RCwLEoQm.jpg',
- alt: 'Three monumental stone busts with the heads that are disproportionately large with somber faces.'
-}, {
- name: 'Blue Nana',
- artist: 'Niki de Saint Phalle',
- description: 'The Nanas are triumphant creatures, symbols of femininity and maternity. Initially, Saint Phalle used fabric and found objects for the Nanas, and later on introduced polyester to achieve a more vibrant effect.',
- url: 'https://i.imgur.com/Sd1AgUOm.jpg',
- alt: 'A large mosaic sculpture of a whimsical dancing female figure in a colorful costume emanating joy.'
-}, {
- name: 'Ultimate Form',
- artist: 'Barbara Hepworth',
- description: 'This abstract bronze sculpture is a part of The Family of Man series located at Yorkshire Sculpture Park. Hepworth chose not to create literal representations of the world but developed abstract forms inspired by people and landscapes.',
- url: 'https://i.imgur.com/2heNQDcm.jpg',
- alt: 'A tall sculpture made of three elements stacked on each other reminding of a human figure.'
-}, {
- name: 'Cavaliere',
- artist: 'Lamidi Olonade Fakeye',
- description: "Descended from four generations of woodcarvers, Fakeye's work blended traditional and contemporary Yoruba themes.",
- url: 'https://i.imgur.com/wIdGuZwm.png',
- alt: 'An intricate wood sculpture of a warrior with a focused face on a horse adorned with patterns.'
-}, {
- name: 'Big Bellies',
- artist: 'Alina Szapocznikow',
- description: "Szapocznikow is known for her sculptures of the fragmented body as a metaphor for the fragility and impermanence of youth and beauty. This sculpture depicts two very realistic large bellies stacked on top of each other, each around five feet (1,5m) tall.",
- url: 'https://i.imgur.com/AlHTAdDm.jpg',
- alt: 'The sculpture reminds a cascade of folds, quite different from bellies in classical sculptures.'
-}, {
- name: 'Terracotta Army',
- artist: 'Unknown Artist',
- description: 'The Terracotta Army is a collection of terracotta sculptures depicting the armies of Qin Shi Huang, the first Emperor of China. The army consisted of more than 8,000 soldiers, 130 chariots with 520 horses, and 150 cavalry horses.',
- url: 'https://i.imgur.com/HMFmH6m.jpg',
- alt: '12 terracotta sculptures of solemn warriors, each with a unique facial expression and armor.'
-}, {
- name: 'Lunar Landscape',
- artist: 'Louise Nevelson',
- description: 'Nevelson was known for scavenging objects from New York City debris, which she would later assemble into monumental constructions. In this one, she used disparate parts like a bedpost, juggling pin, and seat fragment, nailing and gluing them into boxes that reflect the influence of Cubism’s geometric abstraction of space and form.',
- url: 'https://i.imgur.com/rN7hY6om.jpg',
- alt: 'A black matte sculpture where the individual elements are initially indistinguishable.'
-}, {
- name: 'Aureole',
- artist: 'Ranjani Shettar',
- description: 'Shettar merges the traditional and the modern, the natural and the industrial. Her art focuses on the relationship between man and nature. Her work was described as compelling both abstractly and figuratively, gravity defying, and a "fine synthesis of unlikely materials."',
- url: 'https://i.imgur.com/okTpbHhm.jpg',
- alt: 'A pale wire-like sculpture mounted on concrete wall and descending on the floor. It appears light.'
-}, {
- name: 'Hippos',
- artist: 'Taipei Zoo',
- description: 'The Taipei Zoo commissioned a Hippo Square featuring submerged hippos at play.',
- url: 'https://i.imgur.com/6o5Vuyu.jpg',
- alt: 'A group of bronze hippo sculptures emerging from the sett sidewalk as if they were swimming.'
-}];
-```
-
-```css
-button { display: block; margin-bottom: 10px; }
-.Page > * {
- float: left;
- width: 50%;
- padding: 10px;
-}
-h2 { margin-top: 10px; margin-bottom: 0; }
-h3 {
- margin-top: 5px;
- font-weight: normal;
- font-size: 100%;
-}
-img { width: 120px; height: 120px; }
-```
-
-
-
-Notice how `hasPrev` and `hasNext` are used *both* for the returned JSX and inside the event handlers! This handy pattern works because event handler functions ["close over"](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Closures) any variables declared while rendering.
-
-
-
-#### Fix stuck form inputs {/*fix-stuck-form-inputs*/}
-
-When you type into the input fields, nothing appears. It's like the input values are "stuck" with empty strings. The `value` of the first `` is set to always match the `firstName` variable, and the `value` for the second `` is set to always match the `lastName` variable. This is correct. Both inputs have `onChange` event handlers, which try to update the variables based on the latest user input (`e.target.value`). However, the variables don't seem to "remember" their values between re-renders. Fix this by using state variables instead.
-
-
-
-```js
-export default function Form() {
- let firstName = '';
- let lastName = '';
-
- function handleFirstNameChange(e) {
- firstName = e.target.value;
- }
-
- function handleLastNameChange(e) {
- lastName = e.target.value;
- }
-
- function handleReset() {
- firstName = '';
- lastName = '';
- }
-
- return (
-
- );
-}
-```
-
-```css
-h1 { margin-top: 10px; }
-```
-
-
-
-
-
-First, import `useState` from React. Then replace `firstName` and `lastName` with state variables declared by calling `useState`. Finally, replace every `firstName = ...` assignment with `setFirstName(...)`, and do the same for `lastName`. Don't forget to update `handleReset` too so that the reset button works.
-
-
-
-```js
-import { useState } from 'react';
-
-export default function Form() {
- const [firstName, setFirstName] = useState('');
- const [lastName, setLastName] = useState('');
-
- function handleFirstNameChange(e) {
- setFirstName(e.target.value);
- }
-
- function handleLastNameChange(e) {
- setLastName(e.target.value);
- }
-
- function handleReset() {
- setFirstName('');
- setLastName('');
- }
-
- return (
-
- );
-}
-```
-
-```css
-h1 { margin-top: 10px; }
-```
-
-
-
-
-
-#### Fix a crash {/*fix-a-crash*/}
-
-Here is a small form that is supposed to let the user leave some feedback. When the feedback is submitted, it's supposed to display a thank-you message. However, it crashes with an error message saying "Rendered fewer hooks than expected". Can you spot the mistake and fix it?
-
-
-
-Are there any limitations on _where_ Hooks may be called? Does this component break any rules? Check if there are any comments disabling the linter checks--this is where the bugs often hide!
-
-
-
-
-
-```js
-import { useState } from 'react';
-
-export default function FeedbackForm() {
- const [isSent, setIsSent] = useState(false);
- if (isSent) {
- return