Riot brings custom tags to all browsers starting from IE8. Think React + Polymer, but squeezed into 2.5K.

<timer>

  <p>Seconds Elapsed: { time }</p>

  this.time = opts.start || 0

  tick() {
    this.update({ time: ++this.time })
  }

  var timer = setInterval(this.tick, 1000)

  this.on('unmount', function() {
    console.info('timer cleared')
    clearInterval(timer)
  })

</timer>

riot.mount('timer', { start: 0 })

Custom tags lets you build complex views with HTML.

<timetable>
  <timer start="0"></timer>
  <timer start="10"></timer>
  <timer start="20"></timer>
<timetable>

HTML syntax is the de facto language on the web and it's designed for building user interfaces. The syntax is explicit, nesting is inherent to the language and attributes offer a clean way to provide options for custom tags.

• Smallest possible amount of DOM updates and reflows.
• All expressions are pre-compiled cached for high performance.
• No extra HTML root elements or data- attributes.
• No event loops or batching.

• No proprietary event system.
• Event normalization for IE8.
• The rendered DOM can be freely manipulated with other tools.
• Plays well with jQuery.

https://muut.com/riotjs/