title: Cannot find name 'Math'
body: <p>I am learning Angular7 and following tour-of-heroes application. I created InMemoryDataService class and trying to generated id but getting Error 
  "[ts] Cannot find name 'Math'." I also try to add Math package with NPM command but error is still there. </p>
  
  <p>Tried to Install Math package with NPM command . </p>
  
  <pre><code>genId(users: User[] ): number {
      return (&lt;any&gt;users).length &gt; 0 ? Math.max( ...(&lt;any&gt;users).map( user =&gt; user.userId ) ) + 1 : 11;
  }
  </code></pre>
  
  <p>I am not able to use Math class.</p>