index.html

<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Retrosnapper</title>
<script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
</head>
<body>
  <div id="app">
    <p>{{ message }}</p>
    <button v-on:click="upload">Upload Picture</button>
  </div>
  <script src="demo.js">
</body>