title: How to pass an array within a query string in HttpClient?
body: <p>This is my array of actors:</p>
  <pre class="lang-js prettyprint-override"><code>['Elvis', 'Jane', 'Frances']
  </code></pre>
  <p>How to pass this array within a query string in HttpClient?</p>
  <p>I tried to use:</p>
  <p>1)</p>
  <pre class="lang-js prettyprint-override"><code>let params = new HttpParams();
  params = Params.append('actors[]', ['Elvis', 'Jane', 'Frances']);
  this.http.get(url, { params: Params });
  </code></pre>
  <ol start="2">
  <li></li>
  </ol>
  <pre class="lang-js prettyprint-override"><code>let params = new HttpParams().set('actors[]', ['Elvis', 'Jane', 'Frances']);
  this.http.get(url, { params: Params });
  </code></pre>
  <ol start="3">
  <li></li>
  </ol>
  <pre class="lang-js prettyprint-override"><code>let Params = new HttpParams();
  Params = Params.append('actors[]', 'Jane');
  Params = Params.append('actors[]', 'Elvis');
  Params = Params.append('actors[]', 'Frances');
  this.http.get(url, { params: Params }); 
  </code></pre>
  <p>1st and 2nd snippets don't work because of TypeScript error:</p>
  <blockquote>
  <p>[ts] Argument of type 'string[]' is not assignable to parameter of type 'string'.</p>
  </blockquote>
  <p>3rd snippet sends only one item <code>'actors[]': 'Frances'</code></p>