Ionic 2 (Typescript) - issue with variable scope and passing variables

Question

I have this Ionic 2 typescript file. I am trying to set value of a variable from another method. I received undefined on closing the modal.

not able to set the value for coord below.

export class RegisterMapPage {

      .. essential var here..
      public coord: any;

      constructor(
            ....
      ) {}

      ionViewDidLoad() {
            this.initMap()
      }

      initMap() {
            this.geolocation.getCurrentPosition().then((position) => {

                  // // // ..... All map related code here....

                  google.maps.event.addListener(marker, 'dragend', function () {
                        this.coord = marker.getPosition().lat() + ', ' + marker.getPosition().lng();
                        console.log(this.coord); // prints perfectly here.
                  });

            }, (err) => {
                  console.log(err);
            });
      }

      chooseCoord() {
            console.log(this.coord); // undefined ??
            this.viewCtrl.dismiss(this.coords);
      }

}

On marker drag event I update the variable value or coord but the value is undefined when I print it. Can you please help me with the code.

Thanks.

Saravana · Accepted Answer · 2017-07-01 13:30:54Z

1

Because the this inside your callback method is not RegisterMapPage instance since you are using the function() {} syntax for the callback. Use arrow function to get the correct context:

google.maps.event.addListener(marker, 'dragend', () => {
    this.coord = marker.getPosition().lat() + ', ' + marker.getPosition().lng(); // `this` here will point to `RegisterMapPage` instance now that you use arrow function
    console.log(this.coord); // prints perfectly here.
});

answered Jul 1, 2017 at 13:30

Saravana

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1 Comment

Deepankar Over a year ago

Thank you so much. how small was a issue haha. thanks

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