Question

我想我误解了蓝鸟如何取消承诺。我写了一个测试来证明这一点。我如何让它变绿？感谢：

describe('cancellation tests', () => {
  function fakeFetch() {
    return new Promise((resolve, reject) => {
      setTimeout(() => {
        resolve(1);
      }, 100);
    });
  }

  function awaitAndAddOne(p1) {
    return p1.then(res => res + 1);
  }

  it('`cancel` cancels promises higher up the chain', () => {
    const p1 = fakeFetch();
    const p2 = awaitAndAddOne(p1);

    expect(p2.isCancellable()).toBeTruthy();
    p2.cancel();

    return p2
      .then(() => {
        console.error('then');
      })
      .catch(err => {
        console.error(err);
      })
      .finally(() => {
        expect(p2.isCancelled()).toBeTruthy(); // Expected value to be truthy, instead received false
        expect(p1.isCancelled()).toBeTruthy(); 
      });
  });
});

Answer 1

来自here：

默认情况下，取消功能已关闭，您可以使用Promise.config启用它。

好像你没有在Promise上启用cancellation标志：

Promise.config({
  cancellation: true
});

describe(...

Answer 2

@Karen如果正确的话。但问题是你的测试也有点错误

如果你看一下isCancellable方法

Promise.prototype.isCancellable = function() {
    return this.isPending() && !this.isCancelled();
};

这只是检查promise是否为pending且尚未取消。这并不意味着启用取消。

http://bluebirdjs.com/docs/api/cancellation.html

如果你看到上面的网址，则引用下面的

取消功能默认情况下已关闭，您可以使用Promise.config启用它。

如果你看一下cancel方法

Promise.prototype["break"] = Promise.prototype.cancel = function() {
    if (!debug.cancellation()) return this._warn("cancellation is disabled");

现在，如果我将测试更新为正确如下

var Promise = require("bluebird");
var expect = require("expect");

describe('cancellation tests', () => {
    function fakeFetch() {
      return new Promise((resolve, reject) => {
        setTimeout(() => {
          resolve(1);
        }, 100);
      });
    }

    function awaitAndAddOne(p1) {
      return p1.then(res => res + 1);
    }

    it('`cancel` cancels promises higher up the chain', () => {
      const p1 = fakeFetch();
      const p2 = awaitAndAddOne(p1);

      value = p2.isCancellable();
      expect(p2.isCancellable()).toBeTruthy();
      p2.cancel();

      expect(p2.isCancelled()).toBeTruthy(); // Expected value to be truthy, instead received false
      expect(p1.isCancelled()).toBeTruthy(); 
    });
  });

您可以看到取消未启用，它会执行警告代码

执行结果按预期失败

spec.js:46
  cancellation tests
spec.js:46
    1) `cancel` cancels promises higher up the chain
spec.js:78
  0 passing (3m)
base.js:354
  1 failing
base.js:370
  1) cancellation tests
base.js:257
       `cancel` cancels promises higher up the chain:
     Error: expect(received).toBeTruthy()
Expected value to be truthy, instead received
  false
      at Context.it (test/index.test.js:37:36)

现在，如果您更新代码以启用取消

var Promise = require("bluebird");
var expect = require("expect");

Promise.config({
  cancellation: true
});

describe('cancellation tests', () => {
    function fakeFetch() {
      return new Promise((resolve, reject) => {
        setTimeout(() => {
          resolve(1);
        }, 100);
      });
    }

    function awaitAndAddOne(p1) {
      return p1.then(res => res + 1);
    }

    it('`cancel` cancels promises higher up the chain', () => {
      const p1 = fakeFetch();
      const p2 = awaitAndAddOne(p1);

      value = p2.isCancellable();
      expect(p2.isCancellable()).toBeTruthy();
      p2.cancel();

      expect(p2.isCancelled()).toBeTruthy(); // Expected value to be truthy, instead received false
      expect(p1.isCancelled()).toBeTruthy(); 
    });
  });

有效！

如何取消蓝鸟的承诺

2 个答案: