发生错误，尝试链接Java脚本时无法读取未定义的属性'then'

Question

这是我的第一篇文章，如果做错了，抱歉。

我正在尝试将javascript Promise链接在一起，但是当我运行它时，出现错误Uncaught TypeError：无法读取未定义的属性'then'在script.js：108（匿名）@ script.js：108

你知道我在做什么错吗？

    const crates = {
    clothes: 8,
    hats: 20,
    toys: 50,
}

const orderToys = () => {
        new Promise((resolve, reject) => {
        if (crates.toys < 60){
            resolve('yes');
        } else {
            reject('no');
        }
    })
}

const sendMoney = (val) => {
        new Promise((resolve, reject) => {
        if(val === 'yes'){
            resolve('money sent');
        } else {
            reject('no order needed, do not sent money');
        }
    })
}

const orderConfirmed = (val) =>{
        new Promise((resolve, reject) => {
        if(val ==='money sent'){
            resolve('shipped');
        } else {
            reject('No money sent');
        }
    })
}

const delivered = (val) =>{
        new Promise((resolve, reject) => {
        if(val === 'shipped'){
            resolve('order completed');
        } else {
            reject('no order');
        }
    })
};

orderToys()
.then((firstVal) => {
    return sendMoney(firstval);
})
.then((secondVal) =>{
    return orderConfirmed(secondVal);
})
.then((thirdVal) =>{
    return delivered(thirdVal);
})
.then((fourthVal) =>{
    console.log(fourthVal);
})

Answer 1

要么兑现承诺：

const orderToys = () => {
  return new Promise((resolve, reject) => {
    if (crates.toys < 60) {
      resolve('yes');
    } else {
      reject('no');
    }
  })
}

或使用箭头函数的表达形式。

const orderToys = () =>
  new Promise((resolve, reject) => {
    if (crates.toys < 60) {
      resolve('yes');
    } else {
      reject('no');
    }
  });

Answer 2

您没有从函数返回承诺。您需要先返还诺言，然后才能尝试解决它们。希望这会有所帮助。

const crates = {
    clothes: 8,
    hats: 20,
    toys: 50,
}

const orderToys = () => {
       return new Promise((resolve, reject) => {
        if (crates.toys < 60){
            resolve('yes');
        } else {
            reject('no');
        }
    })
}

const sendMoney = (val) => {
       return new Promise((resolve, reject) => {
        if(val === 'yes'){
            resolve('money sent');
        } else {
            reject('no order needed, do not sent money');
        }
    })
}

const orderConfirmed = (val) =>{
       return new Promise((resolve, reject) => {
        if(val ==='money sent'){
            resolve('shipped');
        } else {
            reject('No money sent');
        }
    })
}

const delivered = (val) =>{
      return  new Promise((resolve, reject) => {
        if(val === 'shipped'){
            resolve('order completed');
        } else {
            reject('no order');
        }
    })
};

orderToys()
.then((firstVal) => {
    return sendMoney(firstVal);
})
.then((secondVal) =>{
    return orderConfirmed(secondVal);
})
.then((thirdVal) =>{
    return delivered(thirdVal);
})
.then((fourthVal) =>{
    console.log(fourthVal);
})

Answer 3

如果您使用的是[[Promises，那么您[还应返回诺言，以保留诺言链：

const crates = {
    clothes: 8,
    hats: 20,
    toys: 50,
};

const orderToys = () => {
    return new Promise((resolve, reject) => {
        if (crates.toys < 60) {
            resolve('yes');
        } else {
            reject('no');
        }
    });
};

const sendMoney = (val) => {
    return new Promise((resolve, reject) => {
        if (val === 'yes') {
            resolve('money sent');
        } else {
            reject('no order needed, do not sent money');
        }
    });
};

const orderConfirmed = (val) => {
    return new Promise((resolve, reject) => {
        if (val === 'money sent') {
            resolve('shipped');
        } else {
            reject('No money sent');
        }
    });
};

const delivered = (val) => {
    return new Promise((resolve, reject) => {
        if (val === 'shipped') {
            resolve('order completed');
        } else {
            reject('no order');
        }
    });
};

用法：

orderToys()
    .then((firstVal) => {
        return sendMoney(firstval);
    })
    .then((secondVal) => {
        return orderConfirmed(secondVal);
    })
    .then((thirdVal) => {
        return delivered(thirdVal);
    })
    .then((fourthVal) => {
        console.log(fourthVal);
    });

或者如果您需要使用异步等待形式：

(async function () {
    try {
        const value1 = await orderToys();
        const value2 = await sendMoney(value1);
        const value3 = await orderConfirmed(value2);
        await delivered(value3);
    } catch (e) {
        // Handle errors
        console.log(e);
    }
})();