Code for blogpost "Using JSX for your own lightweight declarative library": https://medium.com/@mikaelbrevik/using-jsx-for-your-own-lightweight-declarative-library-a773d3796475

own-jsx-9.js

const isString = s => typeof s === "string";

function createElement(tag, props, ...children) {
  const el = document.createElement(tag);
  
  // Iterate thorugh all rest arguments as children.
  children.forEach(child => {
    // If string, we make it a text node.
    const node = !isString(child) ? child : document.createTextNode(child);
    // Add the child to the newly created elements.
    el.appendChild(node);
  });
  
  return el;
}
const h1 = <h1>Hello, World</h1>;
// Output HTML
//> <h1>Hello, World</h1>

const list = (
  <ul>
    <li>Peter</li>
    <li>Paul</li>
    <li>Mary</li>
  </ul>
);

// Output HTML
//> <ul><li>Peter</li><li>Paul</li><li>Mary</li></ul>

// Example usage
document.body.appendChild(list);