title: week number of the year by a given date
body: <p>I got the date as follow</p>
  
  <pre><code>const today = new Date();
  </code></pre>
  
  <p>now I need to get the week number of the year. How do I get it on the typescript? </p>
  
  <p>I tried <code>const todayFormated = this.datepipe.transform(today, 'W');</code> but it is returning the week number of the month not year</p>