freeCodeCamp/curriculum/challenges/english/03-front-end-libraries/react/use--for-a-more-concise-conditional.english.md

id, title, challengeType, isRequired, forumTopicId

id	title	challengeType	isRequired	forumTopicId
5a24c314108439a4d4036185	Use && for a More Concise Conditional	6	false	301413

Description

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: {condition && <p>markup</p>} 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.

Instructions

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.

Tests

tests:
  - text: <code>MyComponent</code> should exist and render.
    testString: assert((function() { const mockedComponent = Enzyme.mount(React.createElement(MyComponent)); return mockedComponent.find('MyComponent').length; })());
  - text: When <code>display</code> is set to <code>true</code>, a <code>div</code>, <code>button</code>, and <code>h1</code> should render.
    testString: 'async () => { const waitForIt = (fn) => new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 250)); const mockedComponent = Enzyme.mount(React.createElement(MyComponent)); const state_1 = () => { mockedComponent.setState({display: true}); return waitForIt(() => mockedComponent )}; const updated = await state_1(); assert(updated.find(''div'').length === 1 && updated.find(''div'').children().length === 2 && updated.find(''button'').length === 1 && updated.find(''h1'').length === 1); }; '
  - text: When <code>display</code> is set to <code>false</code>, only a <code>div</code> and <code>button</code> should render.
    testString: 'async () => { const waitForIt = (fn) => new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 250)); const mockedComponent = Enzyme.mount(React.createElement(MyComponent)); const state_1 = () => { mockedComponent.setState({display: false}); return waitForIt(() => mockedComponent )}; const updated = await state_1(); assert(updated.find(''div'').length === 1 && updated.find(''div'').children().length === 1 && updated.find(''button'').length === 1 && updated.find(''h1'').length === 0); }; '
  - text: The render method should use the && logical operator to check the condition of this.state.display.
    testString: getUserInput => assert(getUserInput('index').includes('&&'));

Challenge Seed

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      display: true
    }
    this.toggleDisplay = this.toggleDisplay.bind(this);
  }
  toggleDisplay() {
    this.setState(state => ({
      display: !state.display
    }));
  }
  render() {
    // change code below this line
    return (
       <div>
         <button onClick={this.toggleDisplay}>Toggle Display</button>
         <h1>Displayed!</h1>
       </div>
    );
  }
};

After Test

ReactDOM.render(<MyComponent />, document.getElementById('root'))

Solution

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      display: true
    }
 this.toggleDisplay = this.toggleDisplay.bind(this);
  }
  toggleDisplay() {
    this.setState(state => ({
      display: !state.display
    }));
  }
  render() {
    // change code below this line
    return (
       <div>
         <button onClick={this.toggleDisplay}>Toggle Display</button>
         {this.state.display && <h1>Displayed!</h1>}
       </div>
    );
  }
};