Error: "the cart variable in the ctx object has not been defined"

A project I'm currently working on involves a pizza ordering app, and my current focus is on implementing the Cart feature.

Each user has their own cart, which includes specific details outlined in cart.ts

import { CartItem } from './cartitem';

export class Cart {
    id: string;
    user: string;
    cartitems: CartItem[];
    grand_total: number;
}

Users can add items from the menu, which then become cart items as defined in cartitem.ts:

import { Topping } from './topping';
export class CartItem {
    id: string;
    name: string;
    baseprice: number;
    toppings: Topping[];
    extraprice: number;
    quantity= 1;
    total: number;
}

When an item is added to the cart, a PUT request is made to the API endpoint for the user's cart. The response returns the updated cart contents.

Here is a snippet from my cart.component.ts file:

import { Component, OnInit, ViewChild, Inject, Injector } from '@angular/core';
import { CartItem } from '../shared/cartitem';
import { ActivatedRoute } from '@angular/router';
import { CartService } from '../services/cart.service';
import { map, catchError } from 'rxjs/operators';
import { Cart } from '../shared/cart';

@Component({
  selector: 'app-cart',
  templateUrl: './cart.component.html',
  styleUrls: ['./cart.component.scss']
})
export class CartComponent implements OnInit {

  cart: Cart;

  constructor(
    private route: ActivatedRoute,
    private cartService: CartService,
    @Inject('BaseURL')public BaseURL) { }


  ngOnInit(): void {
    this.updateCart();

  }

  updateCart() {
    this.cartService.mysubject.subscribe((value) => {
      console.log(value);
      this.cartService.getItems().subscribe(response => {
        console.log("Response in cart comp:", response);

        let cartContent = new Cart();
        cartContent.cartitems = response['cartitems'];
        cartContent.id = response['id'];
        cartContent.grand_total = response['grand_total'];
        cartContent.user = response['user'];

        this.cart = cartContent;

        console.log("Cart is:", this.cart);

      });
    });
  }

}

The issue I am facing is that I'm unable to bind the data on the cart.component.html side with 'cart', resulting in the error - ERROR TypeError: "ctx.cart is undefined".

I would appreciate any insights on how to resolve this.

Edit: Below is the content of cart.component.html:

<h2>Cart</h2>
<div>{{cart.user}}</div>
<mat-list dense>
    <mat-list-item *ngFor="let cartitem of cart.cartitems">
        <h2 matLine>Item: {{cartitem.name}}</h2>
        <p matLine>Base Price: ${{cartitem.baseprice}}</p>
        <p matLine [hidden]="cartitem.toppings == []">Extra Toppings:
            <mat-list matLine>
                <mat-list-item matLine *ngFor="let topping of cartitem.toppings">
                    <h4 matLine>{{topping.name}} : + ${{topping.rate}}</h4>
                </mat-list-item>
            </mat-list>
        </p>
        <button mat-mini-fab color="primary"><i class="fa fa-minus-circle"></i></button><div></div><button mat-mini-fab color="primary"><i class="fa fa-plus-circle"></i></button>
    </mat-list-item>

</mat-list>

<div [hidden]="!cart.cartitems"><h2>Subtotal: ${{cart.grand_total}}</h2></div>

<div [hidden]="cart.cartitems">
    <p> Your Cart is Empty!</p>
</div>

Error log message:

ERROR TypeError: "ctx.cart is undefined"
    CartComponent_Template cart.component.html:2
    Angular 26
        executeTemplate
        refreshView
        refreshComponent
        refreshChildComponents
        refreshView
        refreshComponent
        refreshChildComponents
        refreshView
        refreshDynamicEmbeddedViews
        refreshView
        refreshComponent
        refreshChildComponents
        refreshView
        renderComponentOrTemplate
        tickRootContext
        detectChangesInRootView
        detectChanges
        tick
        next
        invoke
        onInvoke
        invoke
        run
        run
        next
        schedulerFn
    RxJS 5
    Angular 8
core.js:6185:19

Answer №1

The issue in the second line of the HTML code is highlighted below

<div>{{cart.user}}</div>

The variable cart is declared in your TypeScript file

cart: Cart;

The value cart.user cannot be displayed because cart is not yet defined when initialized. It will be populated later once the subscription is resolved.

A temporary solution could be to enclose this within an ng-container and apply an *ngIf directive to it.

<ng-container *ngIf="cart">
  <h2...
  ...
  </div>
</ng-container>

This will prevent anything from being displayed until cart has been resolved.

For better code quality, consider replacing all interpolations with getters in the TypeScript file

get cartUser() { return (cart && cart.user) ? cart.user : null }

Your updated HTML would then look like this

<div>{{cartUser}}</div>

Similarly, you may encounter errors with cart.cartitems. Use the following getter method

get cartCartitems() { return (cart && cart.cartitems) ? cart.cartitems : [] }

Replace all occurrences of cart.cartitems with cartCartitems in your HTML code

I hope this explanation helps!

Answer №2

My solution to this issue involved the use of:

cart: Cart = {} as Cart;

in place of:

cart: Cart;

Answer №3

It appears that you may be encountering an issue due to the absence of the ctx context within your HTML. This error could be occurring because the ctx object is not defined in your component, resulting in a binding attempt to a non-existent property. Commonly, this type of error occurs when trying to access a property of an object that is undefined.

For instance:

let someIncorrectObject = undefined;
someIncorrectObject.someValue // ERROR TypeError: "someIncorrectObject.someValue is undefined".

To mitigate this issue, consider binding values in HTML in the following manner:

<div> {{ cart.id }}</div>
, which should resolve the problem.

On a related note, for improved code quality and ease of implementation, it is advisable to structure your code as follows:

// By structuring interfaces like this, there is no need to explicitly instantiate a new class
export interface Cart {
    id: string;
    user: string;
    cartitems: CartItem[];
    grand_total: number;
}

In your code, implement the following approach:

this.cart = {
    cartitems: response['cartitems'],
    id: response['id'],
    grand_total : response['grand_total'],
    user : response['user ']
}

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