Angular Error: The variable was assigned the value of 'undefined' which is incompatible with the expected type of 'ProductInterface[]'. Please update the variable to match the required data type

Encountered the following error message:

An issue arises with the type assignment in my TypeScript file which states - 'Type '{ id: number; name: string; price: number; quantity: number; status: string; description: string; imgaddress: string; } | undefined' is not assignable to type 'ProductInterface[]'. Type 'undefined' is not assignable to type 'ProductInterface[]'.ts(2322)'

while trying to retrieve the product ID from the main link (snapshot). Here's a snippet of my TypeScript file-

import { Component, OnInit } from '@angular/core';
import { ActivatedRoute } from '@angular/router';
import { productsjson } from 'src/data/products';
import { ProductInterface } from 'src/product';
@Component({
  selector: 'app-product-shop',
  templateUrl: './product-shop.component.html',
  styleUrls: ['./product-shop.component.css']
})
export class ProductShopComponent implements OnInit {
  product!: ProductInterface;
  constructor(private route: ActivatedRoute) { }
  ngOnInit(): void {
    const routeParams = this.route.snapshot.paramMap;
    const id = Number(routeParams.get("productId"));//error referenced here as **
    this.product = productsjson.find(product => product.id === id);//another error occurs here
  }
}

This is the structure of my product.ts interface file-

export interface ProductInterface{
    id: number,
    name: string,
    price: number,
    quantity: number,
    status: string,
    description: string,
    imgaddress: string
}

Here is a glimpse into the contents of productsjson.ts file-

export const productsjson=[
    {
        id: 1,
        name: 'Selenium',
        price: 799,
        quantity:2,
        status:'In Stock',
        description:'this course is for automation testing',
        imgaddress:'https://cdn.arstechnica.net/wp-content/uploads/2018/06/macOS-Mojave-Dynamic-Wallpaper-transition.jpg'
    },
    {
        id: 2,
        name: 'Java',
        price: 1299,
        quantity:5,
        status:'In Stock',
        description:'this course is for Java Programming Language',
        imgaddress:'https://cdn.arstechnica.net/wp-content/uploads/2018/06/macOS-Mojave-Dynamic-Wallpaper-transition.jpg'
    }];

Answer №1

It seems like including this code snippet in your ngOnInit method would be beneficial.

ngOnInit(): void {
    const routeParams = this.route.snapshot.paramMap;
    const id = Number(routeParams.get("productId"));
    if (productsjson && productsjson.length > 0) {
       this.product = productsjson.find(product => product.id === id);
    }
  }

Make sure to validate that productsjson is not undefined and contains items before utilizing the find method. Give this a try and share your results with me.

Answer №2

In your ngOnInit, you have the option to check if a value exists using the optional chaining feature introduced in Typescript 3.7.

Your code snippet would look something like this:

ngOnInit(): void {
    const routeParams = this.route.snapshot.paramMap;
    const id = Number(routeParams.get("productId"));**
    this.product = productsjson?.find(product => product.id === id);
}

If you are using TS version prior to 3.7, you will need to include a standard check:

ngOnInit(): void {
  const routeParams = this.route.snapshot.paramMap;
  const id = Number(routeParams.get("productId"));
  if (productjson && productjson.length > 0) { 
    this.product = productsjson.find(product => product.id === id);
  }
}

The issue arises when productjson.find returns an object without a defined interface. In this case, export const productsjson is simply a dictionary without any specific type. To address this, you can either use as in your find method or declare the variable with a specific type.

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