title: error TS2349: Cannot invoke an expression whose type lacks a call signature
body: <p>I am using Angular 2 with TypeScript 2.</p>
  
  <p>When I use</p>
  
  <pre><code>let labels: string[] | number[] = [];
  // let labels: Array&lt;number&gt; | Array&lt;string&gt; = [];
  
  labels.push(1);
  </code></pre>
  
  <p>it gives me error:</p>
  
  <blockquote>
    <p>error TS2349: Cannot invoke an expression whose type lacks a call
    signature.</p>
  </blockquote>