new Vue({
el: '#root',
methods: {
say: function (msg) {
alert(msg)
}
}
})
<html>
<body>
<div id="root">
<button type="button" v-on:click="say('Hello')">Say Hello</button>
</div>
</body>
<script src="https://cdn.jsdelivr.net/npm/vue"></script>
</html>