promises

gistfile1.txt

// non-blocking --- event loop

const resolveAsync = () =>
  new Promise((resolve) => {
    setTimeout(() => {
      resolve('something');
    }, 100);
  });

const rejectAsync = () =>
  new Promise((resolve, reject) => {
    setTimeout(() => {
      reject('!!!error!!!');
    }, 100);
  });

describe('promises', () => {
  it('resolve', () =>
    resolveAsync()
      .then((result) => {
        expect(result).toEqual('something');
      }),
  );

  it('async resolve', async () => {
    const result = await resolveAsync();
    expect(result).toEqual('something');
  });

  it('reject', () =>
    rejectAsync()
      .catch((error) => {
        expect(error).toEqual('!!!error!!!');
      }),
    );

  it('async reject', async () => {
    try {
      await resolveAsync();
    } catch (error) {
      expect(error).toEqual('!!!error!!!');
    }
  });
});