Mutating warn

HTML

<html>

  <head>
    <script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
  </head>

  <body>
    <div>
      <div id="app">
        <h1>{{appText}}&nbsp;</h1>
        <string-bar :inner-text="appText" :on-text-change="onTextChange"></string-bar>
      </div>
    </div>


    <script>
      Vue.component('string-bar', {
        props: ['innerText', 'onTextChange'],
        //Нет реактивного состояния для value, нет v-model
        data: function() {return {
          //text: this.innerText,
          someOtherState: 'some value'
        }},
        methods: {
          onEdit: function(evt) {
            if (this.onTextChange) {
              this.onTextChange(evt.target.value);
            }            
          }
        },
        template: '<input type="text" :value="innerText" @keyup="onTextChange">'
      });

      var app = new Vue({
        el: '#app',
        data: {
          appText: 'some text'
        },
        methods: {
          onTextChange: function(evt) {
            this.appText = evt.target.value;
          }
        }
      });

    </script>
  </body>

</html>