[英]Difference between async/await and async/fixture.whenStable in Angular
I want to know the difference between these two methods for dealing with asynchronous calls in the Angular framework while testing:测试时想知道Angular框架中这两种处理异步调用的方法的区别:
Are they similar?它们相似吗? If not, what is the difference, and when exactly should I use one rather than the other?如果不是,有什么区别,我应该什么时候使用一个而不是另一个?
The first approach of async/await
is stock JavaScript where you want to run the function asynchronously and you can await for promises before carrying over to the next line. async/await
的第一种方法是库存 JavaScript,您希望在其中异步运行 function,您可以等待承诺,然后再转到下一行。
it('it block in an async await way', async(done) => {
await waitForThisFunctionThatReturnsAPromiseBeforeCarringForward();
// do something, make assertions
const x = await getXFromAPromise(); // wait for getXFromAPromise() function to return the promise
// and assign the results to x
// do something, make assertions
done(); // call done to ensure you have run through the whole it block and tell Jasmine you're done
});
The fixture.whenStable
basically waits for all promises in the stack to be resolved before carrying forward with assertions. fixture.whenStable
基本上会等待堆栈中的所有 Promise 都被解决,然后再继续进行断言。
it('demonstration of fixture.whenStable', async(done) => {
// do some actions that will fire off promises
await fixture.whenStable(); // wait until all promises in the call stack have been resolved
// do some more assertions
done(); // call done to tell Jasmine you're done with this test.
});
The done callback is optional but I use it to ensure for better engineering (make sure it traversed through the whole it block). done 回调是可选的,但我使用它来确保更好的工程(确保它遍历整个 it 块)。
Edit ====================编辑 =====================
To handle observables, I use two methods.为了处理 observables,我使用了两种方法。
async/await
with take
and toPromise
operator where you take the first emission and you convert it to a promise. async/await
使用take
和toPromise
操作符,您在其中获取第一个发射并将其转换为 promise。 Feel free to add other operators such as filter
to ignore some emissions before the take(1)
.随意添加其他运算符,例如filter
在take(1)
之前忽略一些排放。
import { take } from 'rxjs/operators';
......
it('should do xyz', async done => {
const x = await component.observable$.pipe(take(1)).toPromise();
expect(x).toBe(....);
done();
});
The other way is to subscribe
with done
callback另一种方法是subscribe
done
回调
it('should do xyz', done => {
component.observable$.subscribe(result => {
expect(result).toBe(...);
// call done here to ensure the test made it within the subscribe
// and did the assertions and to let Jasmine know you're done with the tests
done();
});
});
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