<template> is great, but some people are surprised that it doesn't include any form of parameterization or expressions. The entire process of cloning a template and updating it with data is left up to the developer - it's pretty low level.

That's why my team made the lit-html library, which uses JS tagged template literals to make <template> elements for you, clone them and interpolate data where the JS expressions are, and then update the result really, really fast with new data:

      import {render, html} from 'https://unpkg.com/lit?module';

      let count = 0;
      
      function increment() {
        count++;
        renderCount();
      }   
      
      function renderCount() {
        render(html`
          <p>The count is ${count}</p>
          <button @click=${increment}>Increment</button>
        `, document.body);
      }      
      renderCount();

You can try that out here: https://lit.dev/playground/#gist=1eff9baed1251fc60dd7da8b7f9...

We're also working with Apple on a proposal called Template Instantiation which brings interpolations and updates into HTML itself (though the pandemic and things really stalled that work for the moment).