JSFiddle - React, Tailwind, and code Playground

HTML

<script src="//cdn.jsdelivr.net/mithril/0.1.15/mithril.min.js"></script>

JavaScript

var converter = function(temperature) {
  return [
    m("input[type=number]", {
        oninput: m.withAttr("value", temperature.setCelsius),
        value: temperature.celsius
    }),
    "°C ⇄",
    m("input[type=number]", {
        oninput: m.withAttr("value", temperature.setFahrenheit),
        value: temperature.fahrenheit
    }),
    "°F"
  ]
}

var Temperature = function() {
  this.setCelsius = function(c) {
    this.celsius = c
    this.fahrenheit = Math.round((9/5 * c + 32) * 100) / 100;
  }.bind(this)
  
  this.setFahrenheit = function(f) {
    this.fahrenheit = f
    this.celsius = Math.round((5/9 * (f - 32)) * 100) / 100;
  }.bind(this)
      
  this.setCelsius(0)
}

m.module(document.body, {controller: Temperature, view: converter})