如何阻止 Promise 进一步执行？

Question

所以，我有这个代码库：

const axios = require('axios');

const req = axios.get('https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQYnIfSxQXlLcfndCeenvH8kvgjKfaW51rQpTSR05fOYH6q8Rlt');


Promise.reject(req).then(null, () => {
    console.log('first error --- fired',);

    return new Error('Error')
});


// req is still fine here despite I have rejected it above 

req
    .then(() => {
        console.log('data --- okay');
    }).catch(() => {
    console.log('error ---  fired',);
})

Soo，在查询图像后我拒绝请求实例并期望 req 将处于拒绝状态，但它仍处于 pending 状态，我可以在评论下方访问它。

为什么？

怎样才能完全拒绝？

谢谢！

Answer 1

Promise.reject returns 一个 new promise 并且你传递给 reject 的参数被认为是 reason 拒绝新承诺的原因。它不会将 req 标记为已拒绝的承诺。

您似乎在尝试使用某种取消，本机承诺不支持。您可能会查看 Bluebird promise library which does support cancellation, or as @DaveNewton suggests, leverage axios' own mechanism. You should also read .

这是一个可以在您的场景中使用的简单解决方案（主要受链接问题的影响）：

const cancellable = (other) => {
  let canceled = false;
  const ifCancelled = (res, rej) => val =>
    canceled ? rej(new Error('Canceled')) : res(val);
  const promise = new Promise((resolve, reject) => {
    other.then(ifCancelled(resolve, reject), ifCancelled(reject, reject));
  });
  promise.cancel = () => {
    canceled = true;
  };
  return promise;
};

const req = cancellable(fetch('https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQYnIfSxQXlLcfndCeenvH8kvgjKfaW51rQpTSR05fOYH6q8Rlt'));

req.cancel();

req
  .then(() => {
    console.log('data --- okay');
  }).catch((err) => {
    console.log('error ---  fired', err.message);
  });

如何阻止 Promise 进一步执行？

How may I prevent Promise from further execution?

javascript

es6-promise