title: Dismiss AlertController and stop function call
body: <p>I have a <code>function</code> that displays an alert controller and a button that when clicked updates a field on a firestore database. After 15 seconds the alert is dismissed and another function is fired.</p>
  
  <pre><code>pickupIsRequested(){
      this.pickupRequest.pickupStatus.subscribe(value =&gt; {
          console.log(value);
  
          if(value == true){
              let alert = this.alertCtrl.create({
                  title: 'You have a Pickup Request!',
                  message: '&lt;span&gt;Princess who is 3 minutes away requests a ride&lt;/span&gt;&lt;hr/&gt; You have 15 seconds to accept the request!',
                  buttons: [
                      {
                          text: 'Accept Ride',
                          handler: () =&gt; {
                              this.driver.updateDriverInRide(true, this.driverId);
                          }
                      }
                  ]
              });
              alert.present();
  
              setTimeout(() =&gt; {
                  alert.dismiss();
                  this.driver.updateDriverPickupRequest(false, this.driverId);
              }, 15000);
          }
      }); 
  }
  </code></pre>
  
  <p>How can I stop the <code>function</code> call on the <code>setTimeout</code> method after I click on the alert controller button? Right now if I click on the button the <code>this.driver.updateDriverPickupRequest</code> still fires.</p>