title: Vue class binding with strings?
body: <p>Is there a way to have Vue class binding working with strings?
  So for example:</p>
  
  <pre><code>&lt;div :class={open: target == 'myString'}&gt;&lt;/div&gt;
  var app = new Vue({
    target: null
  })
  </code></pre>
  
  <p>It works when I do it without the quotes</p>
  
  <pre><code>&lt;div :class={open: target == myString}&gt;&lt;/div&gt;
  </code></pre>
  
  <p>but I get the following warning:</p>
  
  <blockquote>
    <p>[Vue warn]: Property or method "myString" is not defined on the instance but referenced during render. Make sure to declare reactive data properties in the data option.</p>
  </blockquote>