react-use-a-ternary-expression-for-conditional-rendering.md

React: Use a Ternary Expression for Conditional Rendering

Before moving on to dynamic rendering techniques, there's one last way to use built-in JavaScript conditionals to render what you want: the ternary operator. 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:

condition ? expressionIfTrue : expressionIfFalse

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.

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.

const inputStyle = {
  width: 235,
  margin: 5
}

class CheckUserAge extends React.Component {
  constructor(props) {
    super(props);
    // change code below this line
    this.state={
      input: '',
      userAge: ''
    }
    // change code above this line
    this.submit = this.submit.bind(this);
    this.handleChange = this.handleChange.bind(this);
  }
  handleChange(e) {
    this.setState({
      input: e.target.value,
      userAge: ''
    });
  }
  submit() {
    this.setState({
      userAge: this.state.input
    });
  }
  render() {
    const buttonOne = <button onClick={this.submit}>Submit</button>;
    const buttonTwo = <button>You May Enter</button>;
    const buttonThree = <button>You Shall Not Pass</button>;
    return (
      <div>
        <h3>Enter Your Age to Continue</h3>
        <input
          style={inputStyle}
          type="number"
          value={this.state.input}
          onChange={this.handleChange} /><br />
        {
          ''===this.state.userAge ? buttonOne : (this.state.userAge<18 ?buttonThree:buttonTwo)/* change code here */
        }
      </div>
    );
  }
};