JSFiddle - React, Tailwind, and code Playground

HTML

<div id="app">
  <button @click="foo = 'bar'">
    Change foo
  </button>
  {{foo}}
</div>

CSS

body {
  color: #fff
}

JavaScript

new Vue({
  el: '#app',
  created() {
    this.foo = 'foo'
  },
  mounted() {
    this.applyFooWatcher()
  },
  methods: {
    applyFooWatcher() {
      this.$watch('foo', function(newVal, oldVal) {
        console.log('Foo changed from ' + oldVal + ' to ' + newVal);
      });
    }
  },
  data: {
    foo: ''
  }
})