Question

我正在处理承诺以及如何设置它们，但是我不明白为什么节点认为我的承诺在错误方面未得到处理...有人可以解释一下吗？

我的简单代码

    // Setting up the Promise
    function add(x, y) {
        return new Promise((response, reject) => {
            // Simple conditional (not perfect, but it just proves a point)
            if(x !== null && y !== null) {
                // I know I could have done 'response(x + y)', but I wanted 
                // to console.log the result also
                var calc = x + y
                response(calc)
                console.log('Calculation: ' + x + ' + ' + y + ' = ' + calc)
            } else {
                // My console does not throw this error?
                reject('One of the inputs was null')
            }
        })
    }
    
    // Function using the Promise
    function calc() {
        add(1, 3)
            .then(res => add(res, 3))
            .then(res => add(res, null))
            .then(res => console.log('Final result: '+res))
            .catch(err => {
                // This error is thrown in console
                throw new Error('Something went horribly wrong')
            })
    }
    
    // Run the code
    calc();

更新

我最初发布的'拒绝'有一个抛出的错误，我明白需要抓住它。

我还想了解为什么在我的控制台中看不到“拒绝”中的字符串？

控制台输出：

Calculation: 1 + 3 = 4
Calculation: 4 + 3 = 7
(node:61950) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 2): Error: Something went horribly wrong
(node:61950) [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

在使用Promise的函数中：

// Function using the Promise
function calc() {
    add(1, 3)
        .then(res => add(res, 3))
        .then(res => add(res, null))
        .then(res => console.log('Final result: '+res))
        .catch(err => {
            // This error is thrown in console
    --->    throw new Error('Something went horribly wrong')
        })
}

与--->合作的行会抛出错误。那个错误没有被发现。通常当你发现错误时，你想用它做一些事情。如果你把它扔回去或抛出另一个错误，那么应该抓住那个投掷。

我对此的处理如下：

// Function using the Promise
function calc() {
    return add(1, 3)
        .then(res => add(res, 3))
        .then(res => add(res, null))
        .then(res => console.log('Final result: '+res))
        .catch(err => {
            // This error is thrown in console
            throw new Error('Something went horribly wrong')
        })
}

calc().catch(err => {
    console.log(error.message); // For example
});

Answer 2

您正在调用reject 和投掷错误。你只需要做其中一个。

您没有显示第一条错误消息。

当您致电.catch时，使用add来解决任何抛出错误也很重要。

当你这样做时： throw new Error('Something went horribly wrong') 你仍然在promise，如果你没有抓到它，你就会造成问题。在Node.js的未来版本中，这将导致您的应用程序退出并显示错误代码。因此，您需要确保始终在承诺中捕获抛出的错误。

使用拒绝

// Setting up the Promise
function add(x, y) {
  return new Promise((response, reject) => {
    // Simple conditional (not perfect, but it just proves a point)
    if(x !== null && y !== null) {
      // I know I could have done 'response(x + y)', but I wanted 
      // to console.log the result also
      var calc = x + y
      response(calc)
      console.log('Calculation: ' + x + ' + ' + y + ' = ' + calc)
    } else {
      // My console does not throw this error?
      reject(new Error('One of the inputs was null'))
    }
  })
}

// Function using the Promise
function calc() {
  return add(1, 3)
    .then(res => add(res, 3))
    .then(res => add(res, null))
    .then(res => console.log('Final result: '+res))
    .catch(err => {
      console.error("Internal Error:", err.message);
      // This error is thrown in console
      throw new Error('Something went horribly wrong')
    })
}

// Run the code
calc().catch((err) => {
  console.error("Outer error:", err.message);
});

使用投掷：

// Setting up the Promise
function add(x, y) {
  return new Promise((response, reject) => {
    // Simple conditional (not perfect, but it just proves a point)
    if(x !== null && y !== null) {
      // I know I could have done 'response(x + y)', but I wanted 
      // to console.log the result also
      var calc = x + y
      response(calc)
      console.log('Calculation: ' + x + ' + ' + y + ' = ' + calc)
    } else {
      // My console does not throw this error?
      throw new Error('One of the inputs was null')
    }
  })
}

// Function using the Promise
function calc() {
  return add(1, 3)
    .then(res => add(res, 3))
    .then(res => add(res, null))
    .then(res => console.log('Final result: '+res))
    .catch(err => {
      console.error("Internal Error:", err.message);
      // This error is thrown in console
      throw new Error('Something went horribly wrong')
    })
}

// Run the code
calc().catch((err) => {
  console.error("Outer error:", err.message);
});

我添加了return add返回的承诺catch，因此您可以try-catch最终错误。

另一种方法是不抛出最终错误并以不同方式处理它。

JS Promises - 为什么我会看到UnhandledPromiseRejectionWarning和DeprecationWarning？

2 个答案: