5.0 KiB
5.0 KiB
id | title | challengeType | isRequired |
---|---|---|---|
5a24c314108439a4d4036185 | Use && for a More Concise Conditional | 6 | false |
Description
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
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; })(), '<code>MyComponent</code> should exist and render.');
- 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, ''When <code>display</code> is set to <code>true</code>, a <code>div</code>, <code>button</code>, and <code>h1</code> should render.''); }; '
- 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, ''When <code>display</code> is set to <code>false</code>, only a <code>div</code> and <code>button</code> should render.''); }; '
- text: The render method should use the && logical operator to check the condition of this.state.display.
testString: getUserInput => assert(getUserInput('index').includes('&&'), 'The render method should use the && logical operator to check the condition of this.state.display.');
Challenge Seed
class MyComponent extends React.Component {
constructor(props) {
super(props);
this.state = {
display: true
}
this.toggleDisplay = this.toggleDisplay.bind(this);
}
toggleDisplay() {
this.setState({
display: !this.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({
display: !this.state.display
});
}
render() {
// change code below this line
return (
<div>
<button onClick={this.toggleDisplay}>Toggle Display</button>
{this.state.display && <h1>Displayed!</h1>}
</div>
);
}
};