承诺捕获行为 [英] Promise catch behavior

问题描述

似乎可以正常运行，而不会抛出错误:

it seems the following works without throwing an error:

var p = new Promise (function (resolve, reject) {
    window.setTimeout(function() {
        reject('ko');
    }, 1000);
});

p.then(function (value) { console.log(value); })
.catch(function () { console.log('catched'); });
// → 'catched'

但这会引发错误:

var p = new Promise (function (resolve, reject) {
    window.setTimeout(function() {
        p.catch(function () { console.log('catched'); });
        reject('ko');
    }, 1000);
});

p.then(function (value) { console.log(value); });
// → 'catched'
// Uncaught (in promise) ko

任何疯狂的猜测为何?

推荐答案

.catch必须直接链接在.then之后.即使以这种方式编写，它仍然会报告未捕获的内容:

The .catch must be directly chained after .then. Even if you write it this way, it will still report uncaught:

var p = new Promise(function(resolve, reject) {
  window.setTimeout(function() {
    //p.catch(function () { console.log('catched'); });
    console.log(p)
    reject('ko');
  }, 1000);
});

p.then(function(value) {
  console.log(value);
});
p.catch(function() {
  console.log('catched');
});

这样做的原因是，如果不这样链接它，则.catch函数将不会收到调用.then

The reason for this is that if you don't chain it like that, the .catch function doesn't receive the return value that gets generated when you call .then

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