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86 changes: 43 additions & 43 deletions content/docs/lists-and-keys.md
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Original file line number Diff line number Diff line change
@@ -1,30 +1,30 @@
---
id: lists-and-keys
title: Lists and Keys
title: Listas y keys
permalink: docs/lists-and-keys.html
prev: conditional-rendering.html
next: forms.html
---

First, let's review how you transform lists in JavaScript.
Primero, vamos a revisar como transformas listas en Javascript.

Given the code below, we use the [`map()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map) function to take an array of `numbers` and double their values. We assign the new array returned by `map()` to the variable `doubled` and log it:
Dado el código de abajo, usamos la función [`map()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map) para tomar un array de `numbers` y duplicar sus valores. Asignamos el nuevo array devuelto por `map()` a la variable `doubled` y la mostramos:

```javascript{2}
const numbers = [1, 2, 3, 4, 5];
const doubled = numbers.map((number) => number * 2);
console.log(doubled);
```

This code logs `[2, 4, 6, 8, 10]` to the console.
Este código muestra `[2, 4, 6, 8, 10]` a la consola.

In React, transforming arrays into lists of [elements](/docs/rendering-elements.html) is nearly identical.
En react, transformar arrays en listas de [elementos](/docs/rendering-elements.html) es casi ídentico.

### Rendering Multiple Components
### Renderizando Múltiples Componentes

You can build collections of elements and [include them in JSX](/docs/introducing-jsx.html#embedding-expressions-in-jsx) using curly braces `{}`.
Puedes hacer colecciones de elementos e [incluirlos en JSX](/docs/introducing-jsx.html#embedding-expressions-in-jsx) usando llaves `{}`.

Below, we loop through the `numbers` array using the JavaScript [`map()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map) function. We return a `<li>` element for each item. Finally, we assign the resulting array of elements to `listItems`:
Debajo, recorreremos el arreglo `numbers` usando la función [`map()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map) de Javascript. Devolvemos un elemento `<li>` por cada ítem . Finalmente, asignamos el array resultante de elementos a `listItems`:

```javascript{2-4}
const numbers = [1, 2, 3, 4, 5];
Expand All @@ -33,7 +33,7 @@ const listItems = numbers.map((number) =>
);
```

We include the entire `listItems` array inside a `<ul>` element, and [render it to the DOM](/docs/rendering-elements.html#rendering-an-element-into-the-dom):
Incluimos entero el array `listItems` dentro de un elemento `<ul>`, y [lo renderizamos al DOM](/docs/rendering-elements.html#rendering-an-element-into-the-dom):

```javascript{2}
ReactDOM.render(
Expand All @@ -42,15 +42,15 @@ ReactDOM.render(
);
```

[**Try it on CodePen**](https://codepen.io/gaearon/pen/GjPyQr?editors=0011)
[**Pruebalo en CodePen**](https://codepen.io/gaearon/pen/GjPyQr?editors=0011)

This code displays a bullet list of numbers between 1 and 5.
Este código muestra una lista de numeros entre 1 y 5.

### Basic List Component
### Componente de Lista Básica

Usually you would render lists inside a [component](/docs/components-and-props.html).
Usualmente renderizarías listas dentro de un [componente](/docs/components-and-props.html).

We can refactor the previous example into a component that accepts an array of `numbers` and outputs an unordered list of elements.
Podemos refactorizar el ejemplo anterior en un componente que acepte un array de `numbers` e imprima una lista desordenada de elementos.

```javascript{3-5,7,13}
function NumberList(props) {
Expand All @@ -70,9 +70,9 @@ ReactDOM.render(
);
```

When you run this code, you'll be given a warning that a key should be provided for list items. A "key" is a special string attribute you need to include when creating lists of elements. We'll discuss why it's important in the next section.
Cuando ejecutes este código, Seras advertido que una key debe ser proporcionada para listar ítems. Una "key" es un atributo especial string que debes incluir al crear listas de elementos. Vamos a discutir porque esto es importante en la próxima sección.

Let's assign a `key` to our list items inside `numbers.map()` and fix the missing key issue.
Vamos a asignar una `key` a nuestra lista de ítems dentro de `numbers.map()` y arreglar el problema de la falta de key.

```javascript{4}
function NumberList(props) {
Expand All @@ -94,11 +94,11 @@ ReactDOM.render(
);
```

[**Try it on CodePen**](https://codepen.io/gaearon/pen/jrXYRR?editors=0011)
[**Pruebalo en CodePen**](https://codepen.io/gaearon/pen/jrXYRR?editors=0011)

## Keys

Keys help React identify which items have changed, are added, or are removed. Keys should be given to the elements inside the array to give the elements a stable identity:
Las keys ayudan a React a identificar que items han cambiado, son agregados, o son eliminados. Las keys deben ser dadas a los elementos dentro del array para darle a los elementos una identidad estable:

```js{3}
const numbers = [1, 2, 3, 4, 5];
Expand All @@ -109,7 +109,7 @@ const listItems = numbers.map((number) =>
);
```

The best way to pick a key is to use a string that uniquely identifies a list item among its siblings. Most often you would use IDs from your data as keys:
La mejor forma de elegir una key es usar un string que idenfique únicamente a un elemento de la lista entre sus hermanos. Con mas frecuencia vas a usar IDs de tus datos como key:

```js{2}
const todoItems = todos.map((todo) =>
Expand All @@ -119,7 +119,7 @@ const todoItems = todos.map((todo) =>
);
```

When you don't have stable IDs for rendered items, you may use the item index as a key as a last resort:
Cuando no tengas IDs estables para renderizar, podrías usar el índice del ítem como una key como último recurso:

```js{2,3}
const todoItems = todos.map((todo, index) =>
Expand All @@ -130,23 +130,23 @@ const todoItems = todos.map((todo, index) =>
);
```

We don't recommend using indexes for keys if the order of items may change. This can negatively impact performance and may cause issues with component state. Check out Robin Pokorny's article for an [in-depth explanation on the negative impacts of using an index as a key](https://medium.com/@robinpokorny/index-as-a-key-is-an-anti-pattern-e0349aece318). If you choose not to assign an explicit key to list items then React will default to using indexes as keys.
No recomendamos usar índices para keys si el orden de los ítems puede cambiar. Esto puede impactar negativamente el rendimiento y puede causar problemas con el estado del componente. Revisa el árticulo de Robin Pokorny para una [explicación en profundidad de los impactos negativos de usar un índice como key](https://medium.com/@robinpokorny/index-as-a-key-is-an-anti-pattern-e0349aece318). Si eliges no asignar una key explícita a la lista de items, React por defecto usara índices como keys.

Here is an [in-depth explanation about why keys are necessary](/docs/reconciliation.html#recursing-on-children) if you're interested in learning more.
Aquí esta una [explicación en profundidad sobre porque las keys son necesarias](/docs/reconciliation.html#recursing-on-children) si estas interesado en aprender más.
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Perhaps Aquí hay instead of Aquí está

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In the original text it is Here is, so for me it should be Aquí está .
It should be Here there is to be translated in Aquí hay in my opinion. What do you think?


### Extracting Components with Keys
### Extracción de Components con Keys

Keys only make sense in the context of the surrounding array.
Las keys solo tienen sentido en el contexto de un array circundante.

For example, if you [extract](/docs/components-and-props.html#extracting-components) a `ListItem` component, you should keep the key on the `<ListItem />` elements in the array rather than on the `<li>` element in the `ListItem` itself.
Por ejemplo, si [extraes](/docs/components-and-props.html#extracting-components) un componente `ListItem`, debes mantener la key en el elemnto `<ListItem />` en el array en lugar de en el elemento `<li>` en el `ListItem` en sí mismo.

**Example: Incorrect Key Usage**
**Ejemplo: Uso Incorrecto de Key**

```javascript{4,5,14,15}
function ListItem(props) {
const value = props.value;
return (
// Wrong! There is no need to specify the key here:
// Mal! No es necesario especificar la key aquí:
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My suggestion: // Mal! Aquí no es necesario especificar la key:

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@gariasf what about No hay necesidad de especificar la key

<li key={value.toString()}>
{value}
</li>
Expand All @@ -156,7 +156,7 @@ function ListItem(props) {
function NumberList(props) {
const numbers = props.numbers;
const listItems = numbers.map((number) =>
// Wrong! The key should have been specified here:
// Mal! La key debería haber sido especificada aquí:
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My suggestion: // Mal! Aquí la key debería haber sido especificada:

<ListItem value={number} />
);
return (
Expand All @@ -173,18 +173,18 @@ ReactDOM.render(
);
```

**Example: Correct Key Usage**
**Ejemplo: Uso Correcto de Key**

```javascript{2,3,9,10}
function ListItem(props) {
// Correct! There is no need to specify the key here:
// Correcto! No hay necesidad de especificar la key aquí:
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My suggestion: // Correcto! Aquí no hay necesidad de especificar la key:

return <li>{props.value}</li>;
}

function NumberList(props) {
const numbers = props.numbers;
const listItems = numbers.map((number) =>
// Correct! Key should be specified inside the array.
// Correcto! La key deberia ser especificada dentro del array.
<ListItem key={number.toString()}
value={number} />
);
Expand All @@ -202,13 +202,13 @@ ReactDOM.render(
);
```

[**Try it on CodePen**](https://codepen.io/gaearon/pen/ZXeOGM?editors=0010)
[**Pruébalo en CodePen**](https://codepen.io/gaearon/pen/ZXeOGM?editors=0010)

A good rule of thumb is that elements inside the `map()` call need keys.
Una buena regla es que los elementos dentro de `map()` necesitan keys.

### Keys Must Only Be Unique Among Siblings
### Las Keys Deben Ser Solo Únicas Entre Hermanos

Keys used within arrays should be unique among their siblings. However they don't need to be globally unique. We can use the same keys when we produce two different arrays:
Las keys usadas dentro de arrays deberían ser únicas entre sus hermanos. Sin embargo, no necesitan ser únicas globalmente. Podemos usar las mismas keys cuando creamos dos arrays diferentes:

```js{2,5,11,12,19,21}
function Blog(props) {
Expand Down Expand Up @@ -246,9 +246,9 @@ ReactDOM.render(
);
```

[**Try it on CodePen**](https://codepen.io/gaearon/pen/NRZYGN?editors=0010)
[**Pruébalo en CodePen**](https://codepen.io/gaearon/pen/NRZYGN?editors=0010)

Keys serve as a hint to React but they don't get passed to your components. If you need the same value in your component, pass it explicitly as a prop with a different name:
Las keys sirven como una sugerencia para React pero no son pasadas a tus componentes. Si necesitas usar el mismo valor en tu componente, pásasela explícitamente como una propiedad con un nombre diferente:

```js{3,4}
const content = posts.map((post) =>
Expand All @@ -259,11 +259,11 @@ const content = posts.map((post) =>
);
```

With the example above, the `Post` component can read `props.id`, but not `props.key`.
Con el ejemplo de arriba, el componente `Post` puede leer `props.id`, pero no `props.key`.

### Embedding map() in JSX
### Incrustando map() en JSX

In the examples above we declared a separate `listItems` variable and included it in JSX:
En los ejemplos de arriba declaramos una variable separada `listItems` y la incluimos en JSX:

```js{3-6}
function NumberList(props) {
Expand All @@ -280,7 +280,7 @@ function NumberList(props) {
}
```

JSX allows [embedding any expression](/docs/introducing-jsx.html#embedding-expressions-in-jsx) in curly braces so we could inline the `map()` result:
JSX permite [incrustar cualquier expresión](/docs/introducing-jsx.html#embedding-expressions-in-jsx) en llaves así que podemos alinear el resultado `map()`:

```js{5-8}
function NumberList(props) {
Expand All @@ -296,6 +296,6 @@ function NumberList(props) {
}
```

[**Try it on CodePen**](https://codepen.io/gaearon/pen/BLvYrB?editors=0010)
[**Pruébalo en CodePen**](https://codepen.io/gaearon/pen/BLvYrB?editors=0010)

Sometimes this results in clearer code, but this style can also be abused. Like in JavaScript, it is up to you to decide whether it is worth extracting a variable for readability. Keep in mind that if the `map()` body is too nested, it might be a good time to [extract a component](/docs/components-and-props.html#extracting-components).
Algunas veces esto resulta en código mas claro, pero este estilo puede ser también abusado. Como en JavaScript, depende de ti decidir cuando vale la pena extraer una variable por legibilidad. Ten en mente que si el cuerpo de `map()` esta muy anidado, puede ser un buen momento para [extraer un componente](/docs/components-and-props.html#extracting-components).