how to use javascript in react js code example

Example 1: how to import js via script in react

import { useEffect } from 'react';

const useScript = url => {
  useEffect(() => {
    const script = document.createElement('script');

    script.src = url;
    script.async = true;

    document.body.appendChild(script);

    return () => {
      document.body.removeChild(script);
    }
  }, [url]);
};

export default useScript;

Example 2: use jsx html

<script src="https://unpkg.com/babel-standalone@6/babel.min.js"></script>

Example 3: javascript react

class TodoApp extends React.Component {
  constructor(props) {
    super(props);
    this.state = { items: [], text: '' };
    this.handleChange = this.handleChange.bind(this);
    this.handleSubmit = this.handleSubmit.bind(this);
  }

  render() {
    return (
      <div>
        <h3>TODO</h3>
        <TodoList items={this.state.items} />
        <form onSubmit={this.handleSubmit}>
          <label htmlFor="new-todo">
            What needs to be done?
          </label>
          <input
            id="new-todo"
            onChange={this.handleChange}
            value={this.state.text}
          />
          <button>
            Add #{this.state.items.length + 1}
          </button>
        </form>
      </div>
    );
  }

  handleChange(e) {
    this.setState({ text: e.target.value });
  }

  handleSubmit(e) {
    e.preventDefault();
    if (this.state.text.length === 0) {
      return;
    }
    const newItem = {
      text: this.state.text,
      id: Date.now()
    };
    this.setState(state => ({
      items: state.items.concat(newItem),
      text: ''
    }));
  }
}

class TodoList extends React.Component {
  render() {
    return (
      <ul>
        {this.props.items.map(item => (
          <li key={item.id}>{item.text}</li>
        ))}
      </ul>
    );
  }
}

ReactDOM.render(
  <TodoApp />,
  document.getElementById('todos-example')
);