See https://facebook.github.io/react/docs/top-level-api.html#react.cloneelement

clone-element.js

import { h } from 'preact';

export default function cloneElement(vnode, props, ...children) {
  return h(
    vnode.nodeName,
    extend(extend({}, vnode.attributes || {}), props),
    children.length ? children : vnode.children
  );
}

// Object.assign() ponyfill
function extend(obj, props) {
  for (let i in props) {
    if (props.hasOwnProperty(i)) {
      obj[i] = props[i];
    }
  }
}