如果你在一个承诺中有一个承诺，你需要两个 catch 吗？

Question

例如，使用 fetch() 进行两次调用（.then() 中的第二个调用），您需要两个 .catch() 还是只需要外部一个就足够了？

我已经尝试复制，但到目前为止还不能。

b = new Promise((resolve, reject) => {
  setTimeout(() => {
    console.log('Solving...');
    resolve('solved');
  }, 3000);
})
  .then(() => {
    new Promise((resolve, reject) => {
      setTimeout(() => {
        console.log('Rejecting...');
        reject('error');
      }, 1000);
    })
      .then(() => null)
      .catch((error) => {
        console.log('Catching error inside.');
        console.log(error);
      });
  })
  .catch((error) => {
    console.log('Catching error outside.');
    console.log(error);
  });

这有效，但如果我删除内部 catch()，我会得到 Unhandled promise rejection 错误

Solving...
Rejecting...
(node:73650) UnhandledPromiseRejectionWarning: error
(node:73650) 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:73650) [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.

Answer 1

No need to multiple catch(). if any error detected then goes to catch()

Answer 2

您需要 return then 块中的承诺才能 catch 它们在一条链中：

b = new Promise((resolve, reject) => {
     setTimeout(() => {
       console.log('Solving...');
       resolve('solved');
     }, 3000);
  })
  .then(() => {
    return new Promise((resolve, reject) => {
      setTimeout(() => {
        console.log('Rejecting...');
        reject('error');
      }, 1000);
    });
  })
  .then(() => null)      // You can get rid of this if you don't have anything to do here
  .catch((error) => {
    console.log('Catching error outside.');
    console.log(error);
  });

这应该也是首选方式。在代码示例中使用嵌套链接会使代码很难阅读。

如果你在一个承诺中有一个承诺，你需要两个 catch 吗？

If you have a promise inside a promise, do you need two catch?

javascript

fetch

es6-promise