heh.js

function h(tag, as, xs) {
  var attrs = Object.entries(as).map(([k, v]) => ` ${k}="${v}"`);

  return `<${tag}${attrs}>${xs.join("")}</${tag}>`;
}

console.log(
  h("div", { id: "foo" }, [
    h("p", { class: "big" }, ["hi", h("p", {}, ["3"])]),
    h("p", {}, ["bye"])
  ])
);

/*
<div id="foo">
    <p class="big">hi
        <p>3</p>
    </p>
    <p>bye</p>
</div>
*/