抓住承诺与承诺的差异

发布于 2025-02-05 09:12:37 字数 938 浏览 0 评论 0原文

new Promise(function(resolve, reject) {
  setTimeout(() => {
    throw new Error("Whoops!");
  }, 1000);
}).catch(alert);

来自 https：//javascript.info/promise-error-romise-error处理代码块将行不通，因为此处的错误不是在执行人运行时生成的错误，而是在以后。

Promise.all([
  new Promise((resolve, reject) => setTimeout(() => resolve(1), 1000)),
  new Promise((resolve, reject) => setTimeout(() => reject(new Error("Whoops!")), 2000)),
  new Promise((resolve, reject) => setTimeout(() => resolve(3), 3000))
]).catch(alert); // Error: Whoops!

为什么捕获量在2秒钟后捕获错误？这看起来与第一个代码块相矛盾，说catch无法正常工作

。

通常，我如何调查所有Promise.los.的承诺？我想索引“承诺的数组”以获取其中1个状态，但不能执行此语法result_promise_all [0]。

最好的话，如果答案可以解释执行顺序，哪种代码何时会触发在Microtask和Macrotask队列上以及何时脱离队列的情况。

原文

From https://javascript.info/promise-error-handling

new Promise(function(resolve, reject) {
  setTimeout(() => {
    throw new Error("Whoops!");
  }, 1000);
}).catch(alert);

It says the catch in this code block will not work because here the error is generated not while the executor is running, but later. So the promise can’t handle it.

However at https://javascript.info/promise-api

Promise.all([
  new Promise((resolve, reject) => setTimeout(() => resolve(1), 1000)),
  new Promise((resolve, reject) => setTimeout(() => reject(new Error("Whoops!")), 2000)),
  new Promise((resolve, reject) => setTimeout(() => resolve(3), 3000))
]).catch(alert); // Error: Whoops!

Why does the catch work to catch the Error after 2 seconds?
This looks like it contradicts the 1st code block saying catch won't work

What is different about Promise.all?

Generally how do I investigate the returned promise from Promise.all? I want to index into that "array of promises" to get the state of 1 of them but can't do this syntax result_promise_all[0].

Best if the answer can explain execution order, when which code triggers what to go on microtask and macrotask queues, and when they get off the queue.

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夏天碎花小短裙 2025-02-12 09:12:37

第一个示例和第二个示例之间的区别只是您在第一个示例中没有拒绝，而在Promise.all中拒绝：

new Promise(function(resolve, reject) {
  setTimeout(() => {
    try {
      throw new Error("Whoops!");
    } catch (e) {
      reject(e)
    }
  }, 1000);
}).catch(alert);



Promise.all([
  new Promise((resolve, reject) => setTimeout(() => resolve(1), 1000)),
  new Promise((resolve, reject) => setTimeout(() => reject(new Error("Whoops!")), 2000)),
  new Promise((resolve, reject) => setTimeout(() => resolve(3), 3000))
]).catch(alert); // Error: Whoops!

The difference between the first and second example is just that you are not rejecting in the first one, while you are rejecting in the Promise.all:

new Promise(function(resolve, reject) {
  setTimeout(() => {
    try {
      throw new Error("Whoops!");
    } catch (e) {
      reject(e)
    }
  }, 1000);
}).catch(alert);



Promise.all([
  new Promise((resolve, reject) => setTimeout(() => resolve(1), 1000)),
  new Promise((resolve, reject) => setTimeout(() => reject(new Error("Whoops!")), 2000)),
  new Promise((resolve, reject) => setTimeout(() => resolve(3), 3000))
]).catch(alert); // Error: Whoops!

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