title: Post request doesn't reach Node from Angular
body: <p>I'm triggering this function called upload() by clicking on submit button on the frontend. </p>
  
  <p>in my app.html:  </p>
  
  <pre><code>&lt;div class="row" style="padding:10px;"&gt;
          &lt;button type="submit" class="btn btn-primary" style="margin-left:10px;" (click)="upload()"&gt;Submit&lt;/button&gt;
      &lt;/div&gt;
  </code></pre>
  
  <p>in my app.ts: </p>
  
  <pre><code>upload() {
  
      this.files = {
        pdf_one: './server/test-pdfs/pdf-sample.pdf',
        pdf_two:  './server/test-pdfs/pdf-sample.pdf',
      };
  
      this.filesToUpload = [];
  
      this.filesToUpload.push(this.files.pdf_one);
      this.filesToUpload.push(this.files.pdf_two);
  
      this.getMergedPDF(this.filesToUpload);
  }
  
  getMergedPDF(filesToUpload): Observable&lt;string&gt; {
          return this.http.post&lt;string&gt;('http://localhost:8081/merge-pdf', JSON.stringify(filesToUpload));
   }
  </code></pre>
  
  <p>I've set breakpoints and the function above is being called just fine. It's just when it gets to the node.js side, nothing is triggered. </p>
  
  <p>Here's how I set the api endpoint on nodejs side: 
      server.js</p>
  
  <pre><code>app.post('/merge-pdf', (req, res) =&gt; {
      this.fileList  = req;
  
      PDFMerge(this.fileList, {output: `${__dirname}/test-pdfs/merged-pdf.pdf`});
      res.send(200);
  });
  
  const server = app.listen(8081, () =&gt; {
      console.log('Listening on port %s...', server.address().port);
  });
  </code></pre>
  
  <p>I was wondering what I could be doing wrong above that the api endpoint is not triggered? </p>
  
  <p>EDIT: </p>
  
  <p>I've tried this: </p>
  
  <pre><code>getMergedPDF(filesToUpload): Observable&lt;string&gt; {
      return this.http.post&lt;string&gt;('http://localhost:8081/merge-pdf', JSON.stringify(filesToUpload))
      .subscribe(data  =&gt; this.mergedUrl = data);
    }
  </code></pre>
  
  <p>But this error happens: </p>
  
  <pre><code>Type 'Subscription' is not assignable to type 'Observable&lt;string&gt;'.
    Property '_isScalar' is missing in type 'Subscription'.'
  </code></pre>