113 lines
2.6 KiB
Markdown
113 lines
2.6 KiB
Markdown
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---
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id: 5a24c314108439a4d403616c
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title: 覆蓋默認的 Props
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challengeType: 6
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forumTopicId: 301399
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dashedName: override-default-props
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---
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# --description--
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在 React 中，設置默認的 props 是一個很有用的特性， 顯式設置組件的 prop 值即可覆蓋默認 props。
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# --instructions--
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`ShoppingCart` 組件現在渲染了一個子組件 `Items`。 該 `Items` 組件有一個默認 `quantity` prop，其值被設置爲整數 `0`。 通過傳入數值 `10` 來覆蓋 `quantity` 的默認 prop。
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**注意：** 請記住，向組件添加 prop 的語法與添加 HTML 屬性類似。 但是，由於 `quantity` 的值是整數，所以它不會加引號，但應該用花括號括起來， 例如`{100}`。 這個語法告訴 JSX 直接將花括號中的值解釋爲 JavaScript。
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# --hints--
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應該渲染 `ShoppingCart` 組件。
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```js
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assert(
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(function () {
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const mockedComponent = Enzyme.mount(React.createElement(ShoppingCart));
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return mockedComponent.find('ShoppingCart').length === 1;
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})()
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);
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```
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應該渲染 `Items` 組件。
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```js
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assert(
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(function () {
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const mockedComponent = Enzyme.mount(React.createElement(ShoppingCart));
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return mockedComponent.find('Items').length === 1;
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})()
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);
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```
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`Items` 組件應該有一個 `{ quantity: 10 }` 的 prop，該 prop 是從 `ShoppingCart` 組件傳遞過去的。
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```js
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(getUserInput) =>
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assert(
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(function () {
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const mockedComponent = Enzyme.mount(React.createElement(ShoppingCart));
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return (
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mockedComponent.find('Items').props().quantity == 10 &&
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getUserInput('index')
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.replace(/ /g, '')
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.includes('<Itemsquantity={10}/>')
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);
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})()
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);
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```
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# --seed--
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## --after-user-code--
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```jsx
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ReactDOM.render(<ShoppingCart />, document.getElementById('root'))
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```
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## --seed-contents--
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```jsx
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const Items = (props) => {
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return <h1>Current Quantity of Items in Cart: {props.quantity}</h1>
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}
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Items.defaultProps = {
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quantity: 0
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}
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class ShoppingCart extends React.Component {
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constructor(props) {
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super(props);
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}
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render() {
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{ /* Change code below this line */ }
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return <Items />
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{ /* Change code above this line */ }
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}
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};
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```
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# --solutions--
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```jsx
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const Items = (props) => {
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return <h1>Current Quantity of Items in Cart: {props.quantity}</h1>
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}
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Items.defaultProps = {
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quantity: 0
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}
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class ShoppingCart extends React.Component {
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constructor(props) {
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super(props);
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}
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render() {
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{ /* Change code below this line */ }
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return <Items quantity = {10} />
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{ /* Change code above this line */ }
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}
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};
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```
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