title: ng-bootstrap typeahead - Error with showing results
body: <p>I'm trying to add ng-bootstrap typeahead to an existing project. I simply added the demo code from the <a href="https://ng-bootstrap.github.io/#/components/typeahead/examples" rel="nofollow noreferrer">ng-bootstrap example</a>. (labelled API
  Simple Typeahead)</p>
  
  <p>When typing in a value the drop down box appears but with no values, although i can highlight a line and clicking the highlighted section fills the text box with the correct value.</p>
  
  <p>It's almost as if the text results are not being written out.</p>
  
  <p>the HTML shows this :</p>
  
  <pre><code>&lt;button class="dropdown-item" role="option" type="button"&gt;
            &lt;!--bindings={
    "ng-reflect-ng-template-outlet-context": "[object Object]",
    "ng-reflect-ng-template-outlet": "[object Object]"
  }--&gt;
        &lt;ngb-highlight _nghost-c2=""&gt;&lt;!----&gt;&lt;/ngb-highlight&gt;
  
        &lt;/button&gt;
  </code></pre>
  
  <p>and chrome debug tools shows this :</p>
  
  <pre><code>ERROR TypeError: _v.context.formatter is not a function
  at Object.eval [as updateDirectives] (NgbTypeaheadWindow.html:3)
  at Object.debugUpdateDirectives [as updateDirectives] (vendor.js?v=1IRb52vH45mb7Eaa5E54mqzy79t-CsOu8zFORpABXoI:17823)
  at checkAndUpdateView (vendor.js?v=1IRb52vH45mb7Eaa5E54mqzy79t-CsOu8zFORpABXoI:17003)
  at callViewAction (vendor.js?v=1IRb52vH45mb7Eaa5E54mqzy79t-CsOu8zFORpABXoI:17368)
  at execEmbeddedViewsAction (vendor.js?v=1IRb52vH45mb7Eaa5E54mqzy79t-CsOu8zFORpABXoI:17326)
  at checkAndUpdateView (vendor.js?v=1IRb52vH45mb7Eaa5E54mqzy79t-CsOu8zFORpABXoI:17004)
  at callViewAction (vendor.js?v=1IRb52vH45mb7Eaa5E54mqzy79t-CsOu8zFORpABXoI:17368)
  at execEmbeddedViewsAction (vendor.js?v=1IRb52vH45mb7Eaa5E54mqzy79t-CsOu8zFORpABXoI:17326)
  at checkAndUpdateView (vendor.js?v=1IRb52vH45mb7Eaa5E54mqzy79t-CsOu8zFORpABXoI:17004)
  at callViewAction (vendor.js?v=1IRb52vH45mb7Eaa5E54mqzy79t-CsOu8zFORpABXoI:17368)
  </code></pre>
  
  <p>and highlights the following:</p>
  
  <pre><code>&lt;ngb-highlight [result]="formatter(result)" [term]="term"&gt;&lt;/ngb-highlight&gt;
  </code></pre>