CODEWITHSUNDEEP
javascripttypescripte2e-testing
Carsten Hilber
Carsten Hilber

Reputation: 296

Typescript Error: Argument of type 'number' is not assignable to parameter of type 'Expected<Promise<number>>'

I have the following function which fails on execution:

it('should show three items', () => {
    const EXPECTED_NUMBER_OF_ITEMS: number = 3;
    const countOfTabElements: Promise<number> = page.listOfTabs.count();
    expect(countOfTabElements).toBe(EXPECTED_NUMBER_OF_ITEMS);
});

It throws the following Error when i execute it:

Argument of type 'number' is not assignable to parameter of type 'Expected>'. (2345)

Any ideas why?

Upvotes: 4

Views: 12580

Answers (3)

Aniruddha Das
Aniruddha Das

Reputation: 21698

I would say to use async and await to handle promise object with minimal code changes.

// no changes to page.po.ts. handle async and await in .spec.ts file
import {browser, by, element} from 'protractor';

export class HomePage {

  navigateTo() {
    return browser.get('/');
  }

  getParagraphText() {
    return element(by.css('cfs-root h1')).getText();
  }

}

//page.e2e-spec.ts
import {HomePage} from './home.po';

describe('ng-app App', () => {
  let page: HomePage;

  beforeEach(() => {
    page = new HomePage();
  });

  it('should display the page heading.', async () => {   // notice the callback is a async function
    page.navigateTo();
    expect(await page.getParagraphText()).toBe('cfs works!');  //here we are using await to handle the promise
    page.getHomeSearchHeading().then((text) => {
      expect(text).toEqual('Universal Data Catalog');
    });
  });

});

Upvotes: 1

Bruno Grieder
Bruno Grieder

Reputation: 29864

Alternatively to @Nitzan Tomer answer you should be able to use async/await (TS >= 2.1 for targeting ES5)

it('should show three items', async () => {
    const EXPECTED_NUMBER_OF_ITEMS: number = 3;
    const value = await page.listOfTabs.count();
    expect(value).toBe(EXPECTED_NUMBER_OF_ITEMS);
});

(as a side note I believe you need a fairly recent version of Mocha to handle promise rejection correctly)

Upvotes: 7

Nitzan Tomer
Nitzan Tomer

Reputation: 164297

Try:

it('should show three items', () => {
    const EXPECTED_NUMBER_OF_ITEMS: number = 3;
    page.listOfTabs.count().then(value => {
        expect(value).toBe(EXPECTED_NUMBER_OF_ITEMS);
    });
});

Upvotes: 6

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