InjectPoint.jsx

import React, { Component } from 'react';
import ReactDOM from 'react-dom';

let instance = null;

export const getTop = () => {
  return instance.getTop();
}

export default class InjectPoint {
  constructor() {
    super();
    instance = this;
  }
  
  render() {
    return <div ref="inject">{this.props.children}</div>;
  }
  
  getTop() {
    const domElement = ReactDOM.findDOMNode(this.refs.inject);
    return domElement.sammink // cant remember how to get the position of a DOM element
  }
}