Using mock data: Typescript is not assignable to type

Question

I'm new to Angular and I believe I've set up my mock data the wrong way and that results in the following error:

Argument of type '{ "name": string; "refCode": string; "contentId": string; "enabled": boolean;  }[]; } | { ...; }' is not assignable to parameter of type 'Item'.

Updated with additional error messages:

Types of property ... are incompatible.
  Type '{ "name": string; "refCode": string; "contentId": string }[]' is not assignable to type 'Item[]'.
    Property ... is missing in type '{ "name": string; "refCode": string; "contentId": string;}' but required in type 'Item'.

Here's my json file contents:

{
  "data": {
    "items": [
      {
        "obj1": "one",
        "obj2": "two",
        "obj3": three
      },
      {
        "obj1": "four",
        "obj2": "five",
        "obj3": siix
        "subCategories": [
          {
          }
        ]
      },
      {
        "name": "Menu Option 1",
        "refCode": "opt1",
        "contentId": "0",
        "subCategories": [
          {}
   
        ]
      },
      {
        "name": "Menu Option 2",
        "refCode": "opt2",
        "contentId": "0"
      },
      {
        "name": "Menu Option 3",
        "refCode": "opt3"
      }
    ]
  }
}

In my service class I import it like this:

import dataItems from './shared/my-items.json';

And declare it like this:

public menuItems: any;

Then I iterate over the items here in my component class:

const optionData = 
this.itemService.getMenuItems().data.items;
const resource = {};
if (itemData && itemData.length > 0) {
  this.items = [];
  itemData.forEach(element => {
    this.itemService.applyItemName(
      element
    );
    this.items.push(element 
  });
  this.itemService.categories = this.itemss;
}

Lastly is the applyItemName() method which adds an item and its children for a given Item:

public applyItemName(item: Item) {
if (item.subCategories && item.subCategories.length > 0) {
  item.subCategories.forEach(subCategory => {
    subCategory.parent = category;
    this.applyItemName(subCategory);
  });
}

}

The model for a Item object is here:

export class Category {
  public subCategories: Items[];
  public contentId: string;


  constructor(subCategories: Item[], enabled: boolean, name: string) 
  {
      this.subCategories = subCategories;
      this.enabled = enabled;
      this.name = name;
    }
  }

As I said, I'm new to this and I'm not sure what I'm missing. Any tips are greatly appreciated.

Answer 1

I think the issue there is childCategories should be optional, since in some childs in your object it is not present. Adding ? at declaration will make it optional:

export class Category {
  public childCategories?: Category[];

Or you could always initialise childCategories as an empty array

  public childCategories: Category[] = [];