PURE ES6 HTML TEMPLATING

cool.js

let index = ({title, name}) => `
  <h1>${title}</h1>
  ${name ? `
    <h2>Hello, ${name}.</h2>
  `:`
    <a href="#">Log in here</a>
  `}

  <div>footer</div>
`;

document.querySelector('div').innerHTML = index({
  title: 'cool page',
  name: 'potch'
});

@asutherland is right! (of course). This is a super gross and way over-clever syntactic hack, and doesn't come close to replacing existing templating libraries, especially in terms of security of interpolated content.