'unhandledRejection' 事件

• reason <Error> | <any> Promise 被拒绝的对象（通常是 Error 对象）。
• promise <Promise> 被拒绝的 promise。

每当 Promise 被拒绝并且在事件循环的一个轮询内没有错误句柄附加到承诺时，则会触发 'unhandledRejection' 事件。 使用 Promise 进行编程时，异常被封装为“被拒绝的 promise”。 拒绝可以使用 promise.catch() 捕获和处理，并通过 Promise 链传播。 'unhandledRejection' 事件对于检测和跟踪尚未处理的被拒绝的 promise 很有用。

process.on('unhandledRejection', (reason, promise) => {
  console.log('Unhandled Rejection at:', promise, 'reason:', reason);
  // 应用程序特定的日志记录，在此处抛出错误或其他逻辑
});

somePromise.then((res) => {
  return reportToUser(JSON.pasre(res)); // 注意错别字 (`pasre`)
}); // 无 `.catch()` 或 `.then()`

以下也将触发 'unhandledRejection' 事件被触发：

function SomeResource() {
  // 最初将加载状态设置为被拒绝的 promise
  this.loaded = Promise.reject(new Error('Resource not yet loaded!'));
}

const resource = new SomeResource();
// resource.loaded 上没有 .catch 或 .then

在此示例情况下，可以将拒绝作为开发人员错误进行跟踪，这通常是其他 'unhandledRejection' 事件的情况。 为了解决此类故障，可以将非操作 .catch(() => { }) 句柄附加到 resource.loaded，这将阻止触发 'unhandledRejection' 事件。

• reason <Error> | <any> The object with which the promise was rejected (typically an Error object).
• promise <Promise> The rejected promise.

The 'unhandledRejection' event is emitted whenever a Promise is rejected and no error handler is attached to the promise within a turn of the event loop. When programming with Promises, exceptions are encapsulated as "rejected promises". Rejections can be caught and handled using promise.catch() and are propagated through a Promise chain. The 'unhandledRejection' event is useful for detecting and keeping track of promises that were rejected whose rejections have not yet been handled.

process.on('unhandledRejection', (reason, promise) => {
  console.log('Unhandled Rejection at:', promise, 'reason:', reason);
  // Application specific logging, throwing an error, or other logic here
});

somePromise.then((res) => {
  return reportToUser(JSON.pasre(res)); // Note the typo (`pasre`)
}); // No `.catch()` or `.then()`

The following will also trigger the 'unhandledRejection' event to be emitted:

function SomeResource() {
  // Initially set the loaded status to a rejected promise
  this.loaded = Promise.reject(new Error('Resource not yet loaded!'));
}

const resource = new SomeResource();
// no .catch or .then on resource.loaded for at least a turn

In this example case, it is possible to track the rejection as a developer error as would typically be the case for other 'unhandledRejection' events. To address such failures, a non-operational .catch(() => { }) handler may be attached to resource.loaded, which would prevent the 'unhandledRejection' event from being emitted.