Error in Angular2: Trying to access the 'Id' property of an undefined variable in Typescript

I encountered this error message:

angular2.dev.js:23925 EXCEPTION: TypeError: Cannot read property 'Id' of null in [

{{ product.Id }}
 in ProductEditComponent@0:68]

This error was thrown with:

//Product-edit.component.ts:

import {Component } from 'angular2/core';
import { IProduct } from './product'
import { ProductService } from './product.service'
import { RouteParams } from 'angular2/router';
@Component({
  template:`<div class="wrapper wrapper-content animated fadeInRight ecommerce"> 
              {{ product.Id }}
            </div>`, 
})
export class ProductEditComponent{
    product: IProduct = null;
    errorMessage: string;
    constructor(private _routeParams: RouteParams, private _productService: ProductService){

    }

    ngOnInit(): void {
        this._productService.getProduct(this._routeParams.get('id'))
            .subscribe(
                product => this.product = product,
                error => this.errorMessage = <any>error);


    }

}

The ProductService code snippet is as follows:

getProduct(id: string): Observable<IProduct> {
    return this._http.get(this._baseUrl + this._getProductUrl + '/' + id)
        .map((response: Response) => <IProduct>response.json())
        .do(data => console.log("All: " + JSON.stringify(data)))
        .catch(this.handleError);
}

Here is the response received from the server:

{"Id":"34d4efcy6","ExternalId":null,"UserId":"testing","ProductProvider":null,"Title":"Flaska vin","Desc":null,"MinDeliveryTime":null,"MaxDeliveryTime":null,"FreightCost":null,"Brand":null}

What could be causing this issue?

Answer №1

Within your component, the issue arises from initializing product as null and then attempting to reference product.Id in your template before an asynchronous call has returned. This results in the error:

Cannot read property 'Id' of null
.

An immediate solution is to utilize the Elvis operator, provided by Angular for scenarios like this. By replacing {{ product.Id }} with {{ product?.Id }} in your template, you can mitigate the error.

However, using the Elvis operator may lead to change detection issues. A more effective approach would be similar to:

export class ProductEditComponent {
  product: Observable<IProduct>; // product is an Observable
  errorMessage: string;
  constructor(private _routeParams: RouteParams, private _productService: ProductService) {
     this._productService.getProduct(this._routeParams.get('id')); 
  }

You can then replace {{product.Id}} with {{(product | async).Id}} in your template, utilizing the AsyncPipe to manage subscription and UI updates seamlessly.

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