JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.4.4/vue.js"></script>
<div id="el">
  <input v-model="form.sale_quantity">
  <input v-model="form.sale_rate">
  <input :value="form.sale_quantity*form.sale_rate" >
</div>

JavaScript

new Vue({
  el: "#el",
  data() {
    return {
      form: {
        sale_quantity: 0,
        sale_rate: 0,
        sale_total: 0
      }
    }
  },
  methods: {
  }
})