buttonFetch.js

class ExampleComponent extends Component {

	constructor() {
		super();

		this.state = {
			data: null
		}
	}

	// This method has an arrow function '=>', which binds 'this' to the method
	// If 'this' isn't bound, this.setState won't be found/work
	handleClick = () => {
	   // Get data from API
	   fetch('https://swapi.co/api/people/?page=1')
		.then(res => res.json())
		.then(jsonData => {
			// Set jsonData to this.state.data
			this.setState({
				data: jsonData
			})
		});
	}

	render() {
		return (
			<div>
				<button onClick={this.handleClick}>Get data</button>
			</div>
		)
	}

}