title: using mixins with vuejs and typescript
body: <p>I would like to use a global mixin using typescript. My mixin looks like this:</p>
  
  <pre><code>Vue.mixin({
    data() {
      return {
        myValue: false
      };
    },
    methods: {
      toggle() {
        this.myValue= !this.myValue;
      }
    }
  });
  </code></pre>
  
  <p>This gives me the following error: <code>TS2339: Property 'myValue' does not exist on type 'Vue'.</code> </p>
  
  <p>If I use the same code inside a compoent <code>Vue.extend({... same code... })</code> everything works fine.</p>