Question

我很难弄清楚 Promise.reject() 如何返回其值。

    const propertyData = {
      id: 1,
      propertyName: '1BR Japanese-style Private Room near Kyoto Station'
    }

    function handleClick(e) {
      getData()
        .then(data => {
            console.log(data.id, data.propertyName); // -> 1, '1BR Japanese-style Private Room near Kyoto Station'
            })
        .catch(err => {
         console.log(err.message); // -> 'Failed to fetch data.' if it's only 'err', it returns the object.
        })

    }

    function getData() {
      return fetchData()
        .then(result => {
          if(result.success){
            return Promise.resolve(result.propertyData);
          } else {
            return Promise.reject(result.message);
          }
        })
    }

    function fetchData() {
      return new Promise((resolve, reject) => {
        let rand = Math.floor(Math.random()*11)
        setTimeout(() => {
                    if(rand >= 3 && rand <= 10){
                        resolve({ success: true, propertyData: propertyData });
                    } else {
                        reject({ success: false, message: 'Failed to fetch data.' });
                    }
            }, 1000)
      })
    }

首先，我预计函数 err 中的错误处理中的 handleClick 将是消息说 'Failed to fetch data' 因为函数 Promise.reject() 中的 getData() 返回 { {1}}。

然而，它似乎返回了对象reject.message。这就是为什么它需要在函数 { success: false, message: 'Failed to fetch data.' } 中设置 err.message 才能获取消息字符串。这是否证明即使您将返回值设置为 handleClick，Promise.reject() 也始终返回对象？

如果是这样，result.message 的行为会有所不同。它返回Promise.resolve()，因此与错误处理不同，它不需要在函数result.propertyData中设置为data.propertyData[key]。

它们，handleClick 和 Promise.resolve() 返回的值是否不同？还是我遗漏了什么？

我希望这能很好地解释我的困惑。谢谢。

Answer 1

const propertyData = {
  id: 1,
  propertyName: "1BR Japanese-style Private Room near Kyoto Station",
};

function handleClick(e) {
  fetchData()
    .then((data) => {
      // We are resolving Object with properties
      // 1. success
      // 2. propertyData (declared on line 1)
      // e.g. Accessing those
      //  - data.success OR - data.propertyData
      const { id, propertyName } = data.propertyData; // Simple destruction of data.propertyData;
      console.log(id, propertyName);
    })
    .catch((err) => {
      console.log(err.message); // -> 'Failed to fetch data.' if it's only 'err', it returns the object.
    });
}

function fetchData() {
  return new Promise((resolve, reject) => {
    let rand = Math.floor(Math.random() * 11);

    setTimeout(() => {
      if (rand >= 3 && rand <= 10) {
        //{ This is what will be the resolved data in .then(data => ) }
        // It can be anything you want string, Object, boolean w/e
        resolve({ success: true, propertyData });
      } else {
        //{ This is what will be the resolved value in .catch()
        // Does not necessarily have to be Object
        // But if you pass only string then in your .catch(err => )  : err here will be string
        // In your case err will be Object with props 'success' and 'message'
        // To access them u go err.message OR err.success
        reject({ success: false, message: "Failed to fetch data." });
      }
    }, 1000);
  });
}

Promise.reject() 返回的值与 Promise.resolve() 不同吗？

1 个答案: