javascript - Bluebird promise 并捕获分支

Question

我想知道 Bluebird 中是否有一种方法 promise .catch抛出的错误，然后处理一些特定的操作而不分支(嵌套 promise )。

说我有

doSomethingAsync()
.then(function (result) {
  if (!result)
    throw new CustomError('Blah Blah');

  if (result == 0)
    throw new CustomError2('Blah Blah Blah');

  return result;
})
.then(function (result) {
  console.log('Success, great!');
})

.catch(CustomError, function (error) {
  // Oh CustomError!
  return saveSomethingAsync();
})
.then(function (saved) {
  // Should only be executed if an CustomError has been thrown
  console.log("Let's try again");
  return doSomethingAsync();
})

.catch(CustomError2, function (error) {
  // Oh CustomError2!
})
.delay(15000) // Don't try again now !
.then(function () {
  // Should only be executed if an CustomError2 has been thrown
  console.log("Let's try again after some long delay");
  return doSomethingAsync();
})

.catch(function (error) {
  // Should catch all random errors of the chain
})

当我执行这段代码时，我得到了几种行为:

• 如果没有错误抛出，我会得到“成功，太棒了!”然后它再次开始“让我们在长时间延迟后重试”
• 如果抛出 CustomError，我会收到“让我们再试一次”
• 如果 CustomError2 抛出异常，我会收到“让我们在长时间延迟后重试”

我无法弄清楚这个流程发生了什么。写这样的东西应该很棒，而不是将错误的特定代码嵌套在新的 promise 链中。

Answer 1

.catch a thrown error and then process some specific actions without branching

没有。因为那是分支。在这里嵌套是完全自然的。您甚至可以使用同步try-catch 比喻来思考这一点，结果是一样的。

I can't figure out what's happening with this flow.

• If no error is thrown, I get "Success, great!" and it start again with "Let's try again after some long delay"

嗯，这很奇怪，因为“让我们再试一次”(没有延迟)是在此之前链接的。您最终应该获得两个日志。您的链将按顺序处理:

doSomethingAsync() // returns a result
 then return result // first callback: continues with it
 then console.log('Success, great!') // next callback: logs something
 catch // is ignored because no rejection
 then console.log("Let's try again"); // next callback: logs something
      return doSomethingAsync();      //                and returns a result
 catch // that result, not being a rejection, is ignored here
 delay // fulfillment is delayed
 then console.log("Let's try again after some long delay"); // next callback again logs
      return doSomethingAsync();                            // and returns a result
 catch // is ignored again

• If a CustomError is thrown, I get "Let's try again"

是的，因为上一个 Promise 的结果 saveSomethingAsync(); 已实现，因此链中的下一个 .then() 回调将执行。

• If a CustomError2 is thrown, I get "Let's try again after some long delay"

是的，因为错误一直冒泡到最终处理的 .catch(CustomError2, …) 。在途中，没有执行任何回调。之后the error was handled ， promise 得到履行，链中的下一个 .then() 调用其回调。

我认为你真正想要的是

doSomethingAsync()
.then(function(result) {
  if (!result)
    // CustomError('Blah Blah');
    // Oh CustomError!
    return saveSomethingAsync();
    .then(function(saved) {
      console.log("Let's try again");
      return doSomethingAsync();
    });
  else if (result == 0)
    // CustomError2('Blah Blah Blah');
    // Oh CustomError2!
    return Promise.delay(15000) // Don't try again now !
    .then(function() {
      console.log("Let's try again after some long delay");
      return doSomethingAsync();
    })
  else
    console.log('Success, great!');
  // return undefined implied
}).catch(function (error) {
  // does catch all random errors of the chain
  // thrown by any of the doSomethingAsync() or of the saveSomethingAsync
})