JS: ERROR SyntaxError: Unexpected token u in JSON at position 0, Nativescript

Question

I have the issue with Json.parse.

I used this only in a model like between:

export class EventsGps {
    eventsgps_id: string;
    latitude: String;
    longitude: string;
    gps_serial: string;  
    event_data: EventData;
    ev_data: any;

    constructor(obj: any) {
        this.ev_data = JSON.parse(obj.event_data);
        this.event_data = this.ev_data;
        this.eventsgps_id = obj.eventsgps_id;
        this.latitude = obj.latitude;
        this.longitude = obj.longitude;
        this.gps_serial = obj.gps_serial;
    }
}

In html I can't show data because show this error, this error only for those data

            this.eventsgps_id = obj.eventsgps_id;
            this.latitude = obj.latitude;
            this.longitude = obj.longitude;
            this.gps_serial = obj.gps_serial;

event_data looks good.

Can you ask me any idea, how to solution this?

When I remove JSON.parse all looks good, only event_data doesn't show because from ws event data arrive like this:

JS:   "event_data": "{\"alarmtype\":\"call\",\"datetime_hb\":\"2018-03-29 12:24:32\",\"hb_serial\":\"aaaa\"}",

Thank you

UPDATE:

I write this service code to get all data:

  public getgps(): Observable<EventsGps[]> {
    let headers = new Headers();
    headers.append('x-access-token', this.auth.getCurrentUser().token);
    return this.http.get(Api.getUrl(Api.URLS.getsgps), {
      headers: headers
    })
      .pipe(map((response: Response) => {
        let res = response.json();
        if (res.StatusCode === 1) {
        } else {
          return res.StatusDescription.map(gps1 => {
           console.log('getgps')
          console.log(gps1)
            return new EventsGps(gps1);
          });
        }
      }))
  }

Result:

: {
JS:   "eventsgps_id": "1",
JS:   "latitude": 50.2029,
JS:   "longitude": 20.3939,
JS:   "gps_serial": "testgps",
JS: }

I write this service code to get all data events

 public getallevents(): Observable<EventsGps[]> {
    let headers = new Headers();
    headers.append('x-access-token', this.auth.getCurrentUser().token);
    return this.http.get(Api.getUrl(Api.URLS.getallevents), {
      headers: headers
    })
      .pipe(map((response: Response) => {
        let res = response.json();
        if (res.StatusCode === 1) {
        } else {
          return res.StatusDescription.map(gps => {
           console.log(gps)
            return new EventsGps(gps);
          });
        }
      }))
  }

Results:

JS: gps events
JS: {
JS:   "id": "1",
JS:   "alarmtype_id": 2,
JS:   "alarmnumber": 5,
JS:   "device_serial": "testgps",
JS:   "acted": 1,
JS:   "user_acted": "31000000000000000000000000000000",
JS:   "dtm_acted": "2018-06-26 03:06:49",
JS:   "event_data": "{\"alarmtype\":\"call\",\"datetime_hb\":\"2018-03-29 12:24:32\",\"hb_serial\":\"aaaa\"}",
JS: }

Obj

constructor(obj: any) {
    console.log('obj')
    console.log(obj)
     ....
        }

Result:

JS: obj
    JS: {
    JS:   "id": "1",
    JS:   "alarmtype_id": 2,
    JS:   "alarmnumber": 5,
    JS:   "device_serial": "testgps",
    JS:   "acted": 1,
    JS:   "user_acted": "31000000000000000000000000000000",
    JS:   "dtm_acted": "2018-06-26 03:06:49",
    JS:   "event_data": "{\"alarmtype\":\"call\",\"datetime_hb\":\"2018-03-29 12:24:32\",\"hb_serial\":\"aaaa\"}",
    JS: }
JS: obj
   : {
    JS:   "eventsgps_id": "1",
    JS:   "latitude": 50.2029,
    JS:   "longitude": 20.3939,
    JS:   "gps_serial": "testgps",
    JS: }

console.log(this.event_data)

Answer 1

Your obj.event_data is undefined at the time you try to parse it.

This will parse without any issue:

JSON.parse("{\"alarmtype\":\"call\",\"datetime_hb\":\"2018-03-29 12:24:32\",\"hb_serial\":\"aaaa\"}");

While this will result in the Unexpected token u in JSON at position 0 error:

JSON.parse(undefined);

---

Update

After looking at your updated question, your first example (gps1) indeed has an undefined event_data property.

const gps1 = {
  "eventsgps_id": "1",
  "latitude": 50.2029,
  "longitude": 20.3939,
  "gps_serial": "testgps",
}

JSON.parse(gps1.event_data); // Unexpected token u in JSON at position 0