gistfile1.txt

import React from "react"
import { render } from "react-dom"

class App extends React.Component {
  state = { highlight: "", pos: "" }
  getText = e => {
    this.setState({
      highlight: window.getSelection().toString(),
      pos: window.getSelection()
    })
  }
  render() {
    const { highlight, pos } = this.state
    return (
      <div>
        <div onClick={this.getText}> I am a body of text</div>
        <h4> Highlighted: </h4>
        <div style={{ background: "yellow" }}>
          TEXT: {highlight}
          <br />
          POSITION:
          {pos.anchorOffset} to
          {pos.extentOffset}
        </div>
      </div>
    )
  }
}

render(<App />, document.getElementById("root"))