new Vue({
el: '#app',
data: {
title: 'Hello world'
},
methods: {sayHello: function(){
this.title = 'WTF';
}}
})
<script src="https://cdn.jsdelivr.net/npm/vue"></script>
<div id="app">
<p v-once>{{title}}</p>
<p>{{sayHello()}}</p>
</div>