title: Array .find() method parameter undefined in vuex
body: <p>I've been struggling with the <code>.find()</code> method in a vuex getter.</p>
  
  <p>I set up a store with a list in state (pages)</p>
  
  <pre class="lang-js prettyprint-override"><code>// state.js
  const state = {
    pages: [{id:1, content:"Page 1"}, {id:2, content:"Page 2"}]
  };
  </code></pre>
  
  <p>And a getter with a <strong>find</strong> method like in this post: <a href="https://stackoverflow.com/questions/52919529/get-object-from-array-with-vuex-getter">Reference</a></p>
  
  <pre class="lang-js prettyprint-override"><code>// getters.js
  const getters = {
    indexPage: state =&gt; {
      let indexPage = state.pages.find(function(page) { // same error with arrow function
        return page.id === 1;
      });
      return indexPage !== undefined ? indexPage : null;
    }
  }
  </code></pre>
  
  <p>I expected to return the first object but after I map the getter (with <em>mapGetters</em>) in a component it throws this error.</p>
  
  <pre><code>TypeError: "page is undefined"
  </code></pre>
  
  <p>Also I tried the same code with <code>.filter()</code> method (which returns an array) but it does work without any errors. This code works:</p>
  
  <pre class="lang-js prettyprint-override"><code>const getters = {
    indexPage: state =&gt; {
      let indexPage = state.pages.filter(page =&gt; page.id === 1);
      return indexPage[0];
    }
  }
  </code></pre>