title: Http request starts leaking
body: <p>I'm using this code to translate each word with <em>translateBack</em></p>
  <pre><code>&lt;span *ngFor=&quot;let word of getWords(); index as i&quot;&gt;
    &lt;button (click)=&quot;speak(word)&quot;
    [matTooltip]=&quot;translateBack(word) | async&quot;&gt;{{word}}&lt;/button&gt;
  &lt;/span&gt;
  </code></pre>
  <p>where <em>translateBack</em> is</p>
  <pre><code>translateBack(word: string) {
    const options = {q: word, source: 'ru-RU', target: 'en-GB'};
    return this._http.post(url + key, options).pipe(
      take(1),
      map((res: any) =&gt; res.data.translations[0].translatedText)
    )
  }
  </code></pre>
  <p>but in my console it shows a never-ending log of http requests. How do just take one? (i tried take(1))</p>