Laravel 5.8 + Vue出现问题以显示信息

Question

我有一个项目，下一个问题，这是我的代码：

  

calculadura.vue

<template>
    <div id="app">
        <label for="quantify">Cantidad Solicitada:</label>
        <input type="number" v-model="quantify" class="form-control">
        <label for="plazo">Plazo Quincenal:</label>
        <select @change="onSelectOption($event)" class="form-control">
            <option value="" disabled selected hidden>Seleccionar una Opción</option>
            <option v-for="i in 12" :value="i">
                {{i}}
            </option>
        </select>
        <br/>
        <h3><span>Por tu prestamo pagarías la cantidad quincenal de: <b class="text-success">$ {{ total }} </b></span></h3>
    </div>
</template>

我的文件

  

“ app.js”

/**
 * First we will load all of this project's JavaScript dependencies which
 * includes Vue and other libraries. It is a great starting point when
 * building robust, powerful web applications using Vue and Laravel.
 */

require('./bootstrap');

window.Vue = require('vue');

/**
 * The following block of code may be used to automatically register your
 * Vue components. It will recursively scan this directory for the Vue
 * components and automatically register them with their "basename".
 *
 * Eg. ./components/ExampleComponent.vue -> <example-component></example-component>
 */

// const files = require.context('./', true, /\.vue$/i);
// files.keys().map(key => Vue.component(key.split('/').pop().split('.')[0], files(key).default));

Vue.component('calculadora-component', require('./components/calculadora.vue').default);
/**
 * Next, we will create a fresh Vue application instance and attach it to
 * the page. Then, you may begin adding components to this application
 * or customize the JavaScript scaffolding to fit your unique needs.
 */

const app = new Vue({
    el: "#app",
    data: {
        quantify: 0,
        total: 0
    },
    methods: {
        onSelectOption(event) {
            this.total = (this.quantify * ((event.target.value * 0.05) + 1))/event.target.value
        }
    }
});

但是不起作用，我想显示{{total}}但不起作用

有什么想法吗？我运行npm run watch进行更新，但是仍然无法正常工作=（