title: forEach Typescript TS2339 "does not exist on type 'void'"
body: <p>Trying to find the intersection of two arrays, why am I getting <code>TS2339:Property 'collection' does not exist on type 'void'</code>?</p>
  
  <p>All arrays are declared in the same class.</p>
  
  <pre><code>this.locations.forEach(function(location) {
      this.collection.locations.forEach(function(id) {
          if(location._id === id) {
              this.display.push(location);
          }
      });
  });
  </code></pre>