281 lines
8.8 KiB
Markdown
281 lines
8.8 KiB
Markdown
---
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id: 5a24c314108439a4d4036187
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title: Use a Ternary Expression for Conditional Rendering
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challengeType: 6
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forumTopicId: 301414
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dashedName: use-a-ternary-expression-for-conditional-rendering
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---
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# --description--
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Before moving on to dynamic rendering techniques, there's one last way to use built-in JavaScript conditionals to render what you want: the <dfn>ternary operator</dfn>. The ternary operator is often utilized as a shortcut for `if/else` statements in JavaScript. They're not quite as robust as traditional `if/else` statements, but they are very popular among React developers. One reason for this is because of how JSX is compiled, `if/else` statements can't be inserted directly into JSX code. You might have noticed this a couple challenges ago — when an `if/else` statement was required, it was always *outside* the `return` statement. Ternary expressions can be an excellent alternative if you want to implement conditional logic within your JSX. Recall that a ternary operator has three parts, but you can combine several ternary expressions together. Here's the basic syntax:
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```jsx
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condition ? expressionIfTrue : expressionIfFalse;
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```
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# --instructions--
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The code editor has three constants defined within the `CheckUserAge` component's `render()` method. They are called `buttonOne`, `buttonTwo`, and `buttonThree`. Each of these is assigned a simple JSX expression representing a button element. First, initialize the state of `CheckUserAge` with `input` and `userAge` both set to values of an empty string.
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Once the component is rendering information to the page, users should have a way to interact with it. Within the component's `return` statement, set up a ternary expression that implements the following logic: when the page first loads, render the submit button, `buttonOne`, to the page. Then, when a user enters their age and clicks the button, render a different button based on the age. If a user enters a number less than `18`, render `buttonThree`. If a user enters a number greater than or equal to `18`, render `buttonTwo`.
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# --hints--
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The `CheckUserAge` component should render with a single `input` element and a single `button` element.
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```js
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assert(
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Enzyme.mount(React.createElement(CheckUserAge)).find('div').find('input')
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.length === 1 &&
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Enzyme.mount(React.createElement(CheckUserAge)).find('div').find('button')
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.length === 1
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);
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```
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The `CheckUserAge` component's state should be initialized with a property of `userAge` and a property of `input`, both set to a value of an empty string.
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```js
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assert(
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Enzyme.mount(React.createElement(CheckUserAge)).state().input === '' &&
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Enzyme.mount(React.createElement(CheckUserAge)).state().userAge === ''
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);
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```
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When the `CheckUserAge` component is first rendered to the DOM, the `button`'s inner text should be Submit.
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```js
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assert(
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Enzyme.mount(React.createElement(CheckUserAge)).find('button').text() ===
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'Submit'
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);
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```
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When a number of less than 18 is entered into the `input` element and the `button` is clicked, the `button`'s inner text should read `You Shall Not Pass`.
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```js
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(() => {
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const mockedComponent = Enzyme.mount(React.createElement(CheckUserAge));
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const initialButton = mockedComponent.find('button').text();
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const enter3AndClickButton = () => {
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mockedComponent
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.find('input')
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.simulate('change', { target: { value: '3' } });
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mockedComponent.find('button').simulate('click');
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mockedComponent.update();
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return mockedComponent.find('button').text();
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};
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const enter17AndClickButton = () => {
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mockedComponent
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.find('input')
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.simulate('change', { target: { value: '17' } });
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mockedComponent.find('button').simulate('click');
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mockedComponent.update();
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return mockedComponent.find('button').text();
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};
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const userAge3 = enter3AndClickButton();
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const userAge17 = enter17AndClickButton();
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assert(
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initialButton === 'Submit' &&
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userAge3 === 'You Shall Not Pass' &&
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userAge17 === 'You Shall Not Pass'
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);
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})();
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```
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When a number greater than or equal to 18 is entered into the `input` element and the `button` is clicked, the `button`'s inner text should read `You May Enter`.
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```js
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(() => {
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const mockedComponent = Enzyme.mount(React.createElement(CheckUserAge));
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const initialButton = mockedComponent.find('button').text();
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const enter18AndClickButton = () => {
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mockedComponent
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.find('input')
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.simulate('change', { target: { value: '18' } });
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mockedComponent.find('button').simulate('click');
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mockedComponent.update();
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return mockedComponent.find('button').text();
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};
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const enter35AndClickButton = () => {
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mockedComponent
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.find('input')
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.simulate('change', { target: { value: '35' } });
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mockedComponent.find('button').simulate('click');
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mockedComponent.update();
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return mockedComponent.find('button').text();
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};
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const userAge18 = enter18AndClickButton();
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const userAge35 = enter35AndClickButton();
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assert(
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initialButton === 'Submit' &&
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userAge18 === 'You May Enter' &&
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userAge35 === 'You May Enter'
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);
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})();
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```
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Once a number has been submitted, and the value of the `input` is once again changed, the `button` should return to reading `Submit`.
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```js
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(() => {
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const mockedComponent = Enzyme.mount(React.createElement(CheckUserAge));
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const enter18AndClickButton = () => {
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mockedComponent
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.find('input')
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.simulate('change', { target: { value: '18' } });
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mockedComponent.find('button').simulate('click');
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mockedComponent.update();
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return mockedComponent.find('button').text();
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};
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const changeInputDontClickButton = () => {
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mockedComponent
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.find('input')
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.simulate('change', { target: { value: '5' } });
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mockedComponent.update();
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return mockedComponent.find('button').text();
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};
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const enter10AndClickButton = () => {
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mockedComponent
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.find('input')
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.simulate('change', { target: { value: '10' } });
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mockedComponent.find('button').simulate('click');
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mockedComponent.update();
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return mockedComponent.find('button').text();
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};
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const userAge18 = enter18AndClickButton();
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const changeInput1 = changeInputDontClickButton();
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const userAge10 = enter10AndClickButton();
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const changeInput2 = changeInputDontClickButton();
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assert(
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userAge18 === 'You May Enter' &&
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changeInput1 === 'Submit' &&
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userAge10 === 'You Shall Not Pass' &&
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changeInput2 === 'Submit'
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);
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})();
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```
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Your code should not contain any `if/else` statements.
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```js
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assert(
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new RegExp(/(\s|;)if(\s|\()/).test(
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Enzyme.mount(React.createElement(CheckUserAge)).instance().render.toString()
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) === false
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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(<CheckUserAge />, document.getElementById('root'));
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```
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## --seed-contents--
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```jsx
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const inputStyle = {
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width: 235,
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margin: 5
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};
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class CheckUserAge extends React.Component {
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constructor(props) {
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super(props);
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// Change code below this line
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// Change code above this line
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this.submit = this.submit.bind(this);
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this.handleChange = this.handleChange.bind(this);
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}
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handleChange(e) {
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this.setState({
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input: e.target.value,
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userAge: ''
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});
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}
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submit() {
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this.setState(state => ({
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userAge: state.input
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}));
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}
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render() {
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const buttonOne = <button onClick={this.submit}>Submit</button>;
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const buttonTwo = <button>You May Enter</button>;
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const buttonThree = <button>You Shall Not Pass</button>;
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return (
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<div>
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<h3>Enter Your Age to Continue</h3>
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<input
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style={inputStyle}
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type='number'
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value={this.state.input}
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onChange={this.handleChange}
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/>
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<br />
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{/* Change code below this line */}
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{/* Change code above this line */}
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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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const inputStyle = {
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width: 235,
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margin: 5
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};
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class CheckUserAge 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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userAge: '',
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input: ''
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};
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this.submit = this.submit.bind(this);
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this.handleChange = this.handleChange.bind(this);
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}
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handleChange(e) {
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this.setState({
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input: e.target.value,
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userAge: ''
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});
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}
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submit() {
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this.setState(state => ({
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userAge: state.input
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}));
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}
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render() {
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const buttonOne = <button onClick={this.submit}>Submit</button>;
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const buttonTwo = <button>You May Enter</button>;
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const buttonThree = <button>You Shall Not Pass</button>;
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return (
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<div>
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<h3>Enter Your Age to Continue</h3>
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<input
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style={inputStyle}
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type='number'
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value={this.state.input}
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onChange={this.handleChange}
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/>
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<br />
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{this.state.userAge === ''
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? buttonOne
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: this.state.userAge >= 18
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? buttonTwo
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: buttonThree}
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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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