<div id="app">
    <input type="text" :value="text" @input="changeInput" />
    <div @click="mychange">Button</div>
  </div>

new Vue({
  el: '#app',

  data() {
    return {
      text: "default"
    };
  },
  methods: {
    changeInput: function(event) {
      alert('changeInput');
      this.text = event.target.value
    },
    
    mychange: function() {
      alert("mychange");
      this.text = "not default";
    }
  }
})