Error: Property '' is not found in type 'Object'. Observable subscribe

Recently delving into Angular2, I encountered a perplexing issue.

I created some mock data like so:

export const WORKFLOW_DATA: Object =
{
    "testDataArray" : [
        { key: "1",              name: "Don Meow",   source: "cat1.png" },
        { key: "2", parent: "1", name: "Roquefort",    source: "cat2.png" },
        { key: "3", parent: "1", name: "Toulouse",   source: "cat3.png" },
        { key: "4", parent: "3", name: "Peppo", source: "cat4.png" },
        { key: "5", parent: "3", name: "Alonzo",     source: "cat5.png" },
        { key: "6", parent: "2", name: "Berlioz", source: "cat6.png" }
    ]
};

This data is then imported in a service and "observed"

import { Injectable } from '@angular/core';

import { WORKFLOW_DATA } from './../mock-data/workflow'
import {Observable} from "rxjs";

@Injectable()
export class ApiService {

  constructor() { }

  getWorkflowForEditor(): Observable<Object>
  {
      return Observable.of( WORKFLOW_DATA );
  }

}

In the component's constructor:

constructor( private apiService: ApiService)
    {
        this.apiService.getWorkflowForEditor().subscribe( WORKFLOW_DATA => {
            console.log( WORKFLOW_DATA);
            console.log( WORKFLOW_DATA.testDataArray );
        } );
    }

The first console.log displays an Object containing the testDataArray property.

However, the second console.log throws a compile time error:

Property 'testDataArray' does not exist on type 'Object'.

Despite still logging an array of objects [Object, Object, ..] as expected.

I am baffled by this behavior and seek clarification on any mistakes I may have made.

Your insights are greatly appreciated!

Answer №1

Typescript is expecting the variable WORKFLOW_DATA to be of type Object in this context:

.subscribe( WORKFLOW_DATA => {} )

based on your declaration:

  getWorkflowForEditor(): Observable<Object>

However, the Object type does not include the property testDataArray. To resolve this, you can either declare that the data may have any properties:

  getWorkflowForEditor(): Observable<any>

or access the property using:

console.log( WORKFLOW_DATA["testDataArray"] );

Answer №2

When you declare in TypeScript:

WORKFLOW_DATA: Object

You are explicitly stating that WORKFLOW_DATA is a simple object with no defined properties. So, when you attempt to access WORKFLOW_DATA.testDataArray, the compiler flags it as a type error.

To enable type checking on WORKFLOW_DATA, you should define an interface that outlines the structure of your object.

Answer №3

If the return type of your method is Observable<Object>, then that will be the type passed when you subscribe. However, there is no testDataArray property on the Object type. You have a few options:

  1. You can type the data and return type differently

    WORKFLOW_DATA: { testDataArray: any } = []
    
    getWorkflowForEditor(): Observable<{ testDataArray: any }>
    
  2. Alternatively, you can type assert the response data to any

    console.log( (<any>WORKFLOW_DATA).testDataArray );
    

Answer №4

Implement Observable

In the service.ts file, make sure to include the following method with the specified subscription. You can choose to refer a specific type object or allow for all types of entries.

fetchData(input: string): Observable<any> {
    let data = {
      input: input,
      language: "en",
      sessionID: "9876543",
    };
    return this.http.post(this.baseURL, data);
  }

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