javascript - 尽管有几个 `try`-`catch` 块，但仍获得 UnhandledPromiseRejectionWarning

Question

我正在使用一个封装了他们的 API 的 3rd 方模块。我有以下代码：

const api = require('3rdpartyapi');

 async function callAPI(params) {
  try {
    let result = await api.call(params);
    return result;
  }
  catch(err) {
    throw err;  //will handle in other function
  }
 }
 
 async function doSomething() {
  try {
    //...do stuff
    let result = await callAPI({a:2,b:7});
    console.log(result);
  }
  catch(err) {
    console.error('oh no!', err);
  }
}

尽管有两个try-catch块，但第 3 方 API 在失去与 homebase 的连接时（经常发生 :( ），会爆炸：

(node:13128) UnhandledPromiseRejectionWarning: FetchError: request to https://www.example.com failed, reason: getaddrinfo ENOTFOUND

其次是：

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)

为什么我的try-没有catch抓住这个？究竟什么是未处理的，以及如何实际处理？

标签： javascriptnode.jspromiseasync-await

Answer 1

关键是 await 仅将“第一层”拒绝转换为错误，但是 promise 内部可以有 promise，并且它们的库可能无法捕获内部拒绝。我已经做了一个概念证明 3rdpartyapi，它可以触发你看到的行为：

(async function () {

// mock 3rdpartyapi
var api = {
    call: async function(){
        await new Promise((resolve, reject) => {
            // why wrap a promise here? but i don't know
            new Promise((innerResolve, innerReject) => {
                innerReject('very sad'); // unfortunately this inner promise fail
                reject('this sadness can bubble up');
            })
        })
    }
};

// your original code
async function callAPI(params) {
    try {
        let result = await api.call(params);
        return result;
    } catch (err) {
        throw err; //will handle in other function
    }
}

async function doSomething() {
    try {
        //...do stuff
        let result = await callAPI({
            a: 2,
            b: 7
        });
        console.log(result);
    } catch (err) {
        console.error('oh no!', err);
    }
}

doSomething();

})();

输出：

$ node start.js
oh no! this sadness can bubble up
(node:17688) UnhandledPromiseRejectionWarning: very sad
(node:17688) 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:17688) [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.