template.js

const app = document.getElementById("app")

const render = (root) => {
  let nodes = []
  
  return function(strings, ...expressions) {
    if (root.childElementCount > 0 && nodes.length > 0 && nodes.length === expressions.length) {
      // update nodes in list with matching expressions

      nodes.forEach((node, idx) => {
        node.innerHTML = expressions[idx]
      })
      
    } else {
      // render initial nodes to the root node
      // set initial node list
      
      root.innerHTML = expressions
      .reduce((htmlString, expr, idx) => {
        return htmlString
          .replace(/>$/, ` data-update="${idx}">`)
          .concat(expr, strings[idx+1])
      }, strings[0])
      
      nodes = document.querySelectorAll("[data-update]")
    }
  }
} 

const html = render(app)

html`
<div>
  <h1>${2/3}</h1>
  <ul>
    <li>${1}</li>
    <li>${1}</li>
    <li>${true ? `<span>true</span>` : `<span>false</span>`}</li>
  </ul>
</div>
`