async/await with generators

async-await.js

// Recursively evaluates generator values 
function customAsync(generatorFn) {
  const generator = generatorFn();

  const resolve = (generatorResult) => {
    const noMoreIterations = generatorResult.done;
    
    if (noMoreIterations) {
      return Promise.resolve(generatorResult.value);
    }

    return Promise.resolve(generatorResult.value)
      .then((newValue) => resolve(generator.next(newValue)))
      .catch((error) => resolve(generator.throw(error)));
  };

  return resolve(generator.next());
}

describe('customAsync', () => {
  it('should await the values of the function', () =>
    customAsync(function* () {
      const result = yield Promise.resolve('My API value');

      expect(result).toBe('My API value');
    }));
});