在Q中学习承诺和例外与拒绝 [英] Learning promises and exceptions vs. rejecting in Q

问题描述

我的印象是，promise中的异常会触发后续的失败处理程序，但我在这段代码中没有看到它：

I'm under the impression that an exception inside a promise will trigger the subsequent fail-handler, but I'm not seeing it happen in this code:

var Q = require('q');

function x() {
  console.log('x');
  var deferred = Q.defer();

  setTimeout(
      function() {
        console.log('resolving x');
        deferred.resolve('hi');
      },
      1000
  );

  return deferred.promise;
}

function y() {
  console.log('y');
  var deferred = Q.defer();

  setTimeout(
      function() {
        console.log('throwing in y');
        throw new Error('Oih!');
      },
      1000
  );

  return deferred.promise;
}

x().then(y).then(
    function () {
      console.log('yes');
    },
    function () {
      console.log('no');
    }
);

我做错了什么，或者我误解了？

Am I doing something wrong, or have I misunderstood?

推荐答案

你正在混合回调和承诺+你有一个延迟反模式的情况。使用 Q.delay 或包装如：

You are mixing callbacks and promises + you have a case of deferred anti-pattern. Either use Q.delay or a wrapper like:

function delay(ms) {
    var d = Q.defer();
    setTimeout(d.resolve, ms);
    return d.promise;
}

现在有超时的promise API，没有理由使用setTimeout ：

Now that there is promise API for timeouts, there is no reason to use setTimeout:

function x() {
    return delay(1000).then(function () {
        console.log("hi");
    });
}

function y() {
    return delay(1000).then(function () {
        console.log('throwing in y');
        throw new Error('Oih!');
    });
}

使用：

x()
.then(y)
.then(function() {
    console.log('yes');
})
.catch(function(e) {
     console.log('no');
});

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