javascript - 链式 promise 不会捕获错误

Question

我正在努力兑现 promise ，到目前为止我偶然发现了这一点:

new Promise((resolve, reject) => {
    setTimeout(() => {
        return resolve()
    }, 400)
}).then(new Promise((resolve, reject) => {
    setTimeout(() => {
        return reject('some error')
    }, 100)
})).then(() => {
    console.log('All promises resolved')
}).catch((err) => {
    console.log('Error: ' + err)
})

我的理解是，这个示例应该显示 Error: some error，第一个 promise 成功解决，第二个 promise 抛出错误。但是当我运行这个(在节点 9.7 中，如果这很重要)时，我收到此错误:

(node:10102) UnhandledPromiseRejectionWarning: some error
(node:10102) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:10102) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
All promises resolved

我的.catch()似乎不起作用，是不是有问题？

Answer 1

您实际上传递的是 promise ，而不是函数。

你应该这样编写代码:

new Promise((resolve, reject) => {
    setTimeout(() => {
        resolve()
    }, 400)
}).then(() => new Promise((resolve, reject) => {
    setTimeout(() => {
        reject(new Error('some error'))
    }, 100)
})).then(() => {
    console.log('All promises resolved')
}).catch((err) => {
    console.log('Error: ' + err)
})