window-size.js

import React from "react";

let hasWindow = typeof window !== "undefined";

class WindowSize extends React.Component {
  state = {
    width: hasWindow && window.innerWidth,
    height: hasWindow && window.innerHeight,
  };

  resize = () =>
    this.setState({
      width: window.innerWidth,
      height: window.innerHeight
    });

  componentDidMount() {
    window.addEventListener("resize", this.resize);
  }

  componentWillUnmount() {
    window.removeEventListener("resize", this.resize);
  }

  render() {
    return this.props.children(this.state);
  }
}

export default WindowSize;