145 lines
4.2 KiB
Markdown
145 lines
4.2 KiB
Markdown
![]() |
---
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id: 5a24c314108439a4d4036185
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title: Use && for a More Concise Conditional
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challengeType: 6
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forumTopicId: 301413
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dashedName: use--for-a-more-concise-conditional
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---
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# --description--
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The if/else statements worked in the last challenge, but there's a more concise way to achieve the same result. Imagine that you are tracking several conditions in a component and you want different elements to render depending on each of these conditions. If you write a lot of `else if` statements to return slightly different UIs, you may repeat code which leaves room for error. Instead, you can use the `&&` logical operator to perform conditional logic in a more concise way. This is possible because you want to check if a condition is `true`, and if it is, return some markup. Here's an example:
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`{condition && <p>markup</p>}`
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If the `condition` is `true`, the markup will be returned. If the condition is `false`, the operation will immediately return `false` after evaluating the `condition` and return nothing. You can include these statements directly in your JSX and string multiple conditions together by writing `&&` after each one. This allows you to handle more complex conditional logic in your `render()` method without repeating a lot of code.
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# --instructions--
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Solve the previous example again, so the `h1` only renders if `display` is `true`, but use the `&&` logical operator instead of an `if/else` statement.
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# --hints--
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`MyComponent` should exist and render.
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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(MyComponent));
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return mockedComponent.find('MyComponent').length;
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})()
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);
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```
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When `display` is set to `true`, a `div`, `button`, and `h1` should render.
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```js
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async () => {
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const waitForIt = (fn) =>
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new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 250));
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const mockedComponent = Enzyme.mount(React.createElement(MyComponent));
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const state_1 = () => {
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mockedComponent.setState({ display: true });
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return waitForIt(() => mockedComponent);
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};
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const updated = await state_1();
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assert(
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updated.find('div').length === 1 &&
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updated.find('div').children().length === 2 &&
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updated.find('button').length === 1 &&
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updated.find('h1').length === 1
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);
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};
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```
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When `display` is set to `false`, only a `div` and `button` should render.
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```js
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async () => {
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const waitForIt = (fn) =>
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new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 250));
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const mockedComponent = Enzyme.mount(React.createElement(MyComponent));
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const state_1 = () => {
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mockedComponent.setState({ display: false });
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return waitForIt(() => mockedComponent);
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};
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const updated = await state_1();
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assert(
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updated.find('div').length === 1 &&
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updated.find('div').children().length === 1 &&
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updated.find('button').length === 1 &&
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updated.find('h1').length === 0
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);
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};
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```
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The render method should use the && logical operator to check the condition of this.state.display.
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```js
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(getUserInput) => assert(getUserInput('index').includes('&&'));
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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(<MyComponent />, document.getElementById('root'))
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```
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## --seed-contents--
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```jsx
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class MyComponent extends React.Component {
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constructor(props) {
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super(props);
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this.state = {
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display: true
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}
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this.toggleDisplay = this.toggleDisplay.bind(this);
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}
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toggleDisplay() {
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this.setState(state => ({
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display: !state.display
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}));
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}
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render() {
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// Change code below this line
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return (
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<div>
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<button onClick={this.toggleDisplay}>Toggle Display</button>
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<h1>Displayed!</h1>
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</div>
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);
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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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class MyComponent extends React.Component {
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constructor(props) {
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super(props);
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this.state = {
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display: true
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}
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this.toggleDisplay = this.toggleDisplay.bind(this);
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}
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toggleDisplay() {
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this.setState(state => ({
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display: !state.display
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}));
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}
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render() {
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// Change code below this line
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return (
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<div>
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<button onClick={this.toggleDisplay}>Toggle Display</button>
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{this.state.display && <h1>Displayed!</h1>}
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</div>
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);
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}
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};
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```
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