Angular 4: How to call catch and callback function in it to handle error. Arrow function, manage errors in get or post services.

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How to call catch and callback function in it to handle error

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Angular 4: How to call catch and callback function in it to handle error

Angular 4: how to redirect if API returns an error?

How to manage errors in get or post services

Need to import

import { Router } from ‘@angular/router’;

import { Observable } from ‘rxjs/Rx’;

 Need to mention router in constructor

constructor(private router: Router, private http: Http) {}

Sometimes when you call catch without using arrow function like below

getUserList() {

                return this.http.get(this.constURL + ‘/loans/all’, this.headerOptions)

                .catch(this.handleError);

}

 

handleError(error: Response) {

                if (error.status == 500) {     

                  this.router.navigate([‘/login’]);

                } else {

                  return Observable.throw(error);

                }

}

 

Then it gives error of

 

ERROR TypeError: Cannot read property ‘navigate’ of undefined not getting this

 

Because in handleError function this object is not accessible. If you console this.router then you will get undefined.

So this object not working and not getting router all available methods

So you have to use arrow function here like below

 

getUserList() {

                return this.http.get(this.constURL + ‘/loans/all’, this.headerOptions)

                .catch(error => {

                  return this.handleError(error);

                });

}

 

handleError(error: Response) {

                if (error.status == 500) {     

                  this.router.navigate([‘/login’]);

                } else {

                  return Observable.throw(error);

                }

}

 

Also if you have not mentioned return for handlerError function then it will throw error again like

Argument of type ‘(error: any) => void’ is not assignable to parameter of type

So it’s necessary to type return for handlerError function.

 

I searched a lot for my solution after spending half a day i can able to find solution.

Nowhere given simple/full solution.

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24 thoughts on “Angular 4: How to call catch and callback function in it to handle error. Arrow function, manage errors in get or post services.”

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