filter out only `on` event props from react component

a.js

// ...
renderMenu() {
  const { children, ...rest } = this.props || {};

  // only store props that startWith `on` in case the parent component
  // wants to send event callbacks down, for subsequent use.
  const eventProps = Object.keys(rest)
    .filter(key => key.substr(0, 2) === 'on') // if startsWith 'on' (ie. onMouseOver)
    .reduce((obj, key) => Object.assign(obj, { [key]: rest[key] }), {});
  // ...
}

could add an additional check to ensure that the 2nd index is an uppercase. mebe key.substr(0, 2) === 'on' && key.substr(2,1) === key.substr(2,1).toUpperCase()