MousePosition.js

class MousePosition extends Component {
	constructor(props) {
		super(props);

		this.onMouseMove = this._onMouseMove.bind(this);
		this.state = { x: 0, y: 0 };
	}

	componentDidMount() {
		document.addEventListener('mousemove', this.onMouseMove);
	}

	_onMouseMove(e) {
		this.setState(() => ({
			x: e.clientX,
			y: e.clientY,
		}));
	}

	render() {
		const { x, y } = this.state;
		const { children } = this.props;

		return children({ x, y });
	}
}