react-portal onOpen Not Firing

[padlock98]

Been trying to migrate from react-portal from v2 to v4, due to recent upgrade of React to 16.8.6.

Stucked at Portal, whereby the dialog box doesn't show up even when isOpen=true. Found out that onOpen is not firing. Any suggestion on how should I change the codes?

import * as React from 'react';
import { Portal } from 'react-portal';

import 'dialog-polyfill/dialog-polyfill.css';
import 'dialog-polyfill/dialog-polyfill.js';

import { Dialog, DialogTitle, DialogContent, DialogActions, Button } from 'react-mdl';

class Confirm extends React.Component {
  onOpen() {
    if (!this.dialog.showModal) {
      dialogPolyfill.registerDialog(this.dialog);
    }

    this.dialog.showModal();
  }

  closeDialog() {
    this.dialog.close();
    this.portal.closePortal();
  }

  render() {
    const props = this.props;

    return (
      <Portal ref={c => this.portal = c} onOpen={this.onOpen.bind(this)} isOpen={Boolean(props.callback)} {...props}>
        <dialog ref={c => this.dialog = c} className="mdl-dialog" style={props.style}>
          <DialogTitle>{props.title}</DialogTitle>
          <DialogContent>
            {props.message}
          </DialogContent>
          <DialogActions>
            <Button type='button' onClick={() => {this.closeDialog(); props.confirm();}}>Confirm</Button>
            <Button type='button' onClick={() => {this.closeDialog(); props.dismissConfirmation();}}>Cancel</Button>
          </DialogActions>
        </dialog>
      </Portal>
    );
  }
}

export default Confirm;

Expected Result: A confirmation dialog box to pop up.

From browser, already can see the dialog box is there by modifying the css.