title: How to get length of array in template syntax
body: <p>I am trying to evaluate the below in template syntax which is an array:</p>
  
  <pre><code>FAIL 
  {{ cols.length }}
  </code></pre>
  
  <p>I get the below error.  </p>
  
  <pre><code>platform-browser.umd.js:1900 ORIGINAL EXCEPTION: TypeError: Cannot read property 'length' of undefined
  </code></pre>
  
  <p>But I do iterate so I know that portion works:</p>
  
  <pre><code>      SUCCESS
       &lt;th *ngFor="let h of cols"&gt; 
          {{h}}
        &lt;/th&gt;
  </code></pre>