JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://unpkg.com/[email protected]/dist/vue.js"></script>
<div id="app">
  {{item}}
</div>

JavaScript

someExternalObject = { thing: 'some initial text' }

var vm = new Vue({
  el: '#app',
  computed: {
    item() {
      return someExternalObject.thing;
    }
  },
  created()
  {
  	// Give the external object a scoped reference
  	this.someExternalObject = someExternalObject;
    
  	this.$watch('someExternalObject.thing', function (newVal, oldVal)
		{
			console.log("Watched:", newVal, oldVal);
		}, { deep: true, immediate: true }); 
  }
})

setTimeout(() => {
  someExternalObject.thing = 'some updated text';
  console.log(someExternalObject.thing);
}, 1000)