FileReader() sample

filereader.js

handleFileChoose() {
  const fileReader = new FileReader();
  const imgUrl = document.getElementById('openFile').files[0];
  if (imgUrl) {
    fileReader.readAsDataURL(imgUrl);
    fileReader.onloadend = () => {
      document.getElementById('avatarImg').src = fileReader.result;
    }
  }
}

index.html

<div>  
  <img id="avatarImg" />
  <label htmlFor="openFile">EDIT</label>
  <input id="openFile" type="file" onChange={() => this.handleFileChoose()} />
</div>