<div id="app">
   count: {{ count }}
</div>

<script src="https://unpkg.com/vue@next"></script>
<script>
const state = Vue.reactive({
   count: 0
});

const vm = app.mount('#app')
</script>

为什么不出来count: 0呢？

<div id="app">
</div>

<script src="https://unpkg.com/vue@next"></script>
<script>
const state = reactive({
   count: 0
})

</script>