如何解决承诺拒绝不能正确传播错误
我收到一个复杂的对象,假设它看起来像这样:
complexObject: {
fruits: string[],vegetables: string[],milk: [] | [{
expirationDate: string,quantity: string
}]
}
因此,逻辑是,当我收到一个空对象(milk
只是[]
)时,verifyObject
方法将返回未定义的(进一步的逻辑更加复杂,并且必须收到未定义的...);使用空/未定义对象调用该方法时,情况相同。
牛奶的唯一验证应如下所示:
如果我们有牛奶,那么它需要同时有quantity
和expirationDate
,否则应该返回false。
问题是,当我发送这样的对象时:
{
'fruits': ['apples','bananas'],'vegetables': ['tomatoes'],'milk': [{
'quantity': '10'
}]
}
在checkAndAssign
方法中,它会看到错误并打印console.log
,但它不会在那里停止,它将对象添加到result
中。
另外,在verifyObject
方法中,它将进入catch块,但在上方它不会引发错误,而是将解决promise,返回结果...
当我收到错误消息并传播错误时,我想停止执行...
这是代码:
verifyObject(complexObject) {
return new Promise((resolve,reject) => {
const result = {};
const propertiesEnum = ['fruits','vegetables','milk'];
if (!complexObject) {
resolve({ result: undefined });
} else {
this.checkAndAssign(complexObject,result)
.catch((err) => {
console.log('enter error');
reject({ message: err });
})
if (!Object.keys(result).length) {
console.log('resolve with undefined');
resolve({ result: undefined });
}
console.log('resolve good');
resolve({ result });
}
})
}
private checkAndAssign(complexObject,result) {
return new Promise((resolve,reject) => {
for (const property of complexObject) {
if(complexObject[property] && Object.keys(complexObject[property]).length)
if(property === 'milk' && this.verifyMilk(complexObject[property]) === false) {
console.log('rejected');
reject('incomplete');
}
Object.assign(result,{[property]: complexObject[property]})
console.log('result is...:>',result);
}
console.log('final result:>',result);
resolve(result);
});
}
private verifyMilk(milk:any): boolean {
for(const item of milk) {
if(!(item['expirationDate'] && item['quantity'])) {
return false;
}
}
return true;
}
解决方法
调用reject
不会终止您从中调用的功能。 reject
只是一个普通的函数调用。调用完成后,调用它的函数将继续。
如果您不想这样做,请使用return
:
private checkPropertyAndAssignValue(complexObject,result) {
return new Promise((resolve,reject) => {
for (const property of complexObject) {
if(complexObject[property] && Object.keys(complexObject[property]).length)
if(property === 'milk' && this.verifyMilk(complexObject[property]) === false) {
console.log('rejected');
reject('incomplete');
return; // <================================================ here
}
Object.assign(result,{[property]: complexObject[property]})
console.log('result is...:>',result);
}
console.log('final result:>',result);
resolve(result);
});
}
然后verifyObject
需要等待checkPropertyAndAssignValue
的诺言的兑现。 verifyObject
的代码成为显式承诺创建反模式的牺牲品:它不应该使用new Promise
,因为它已经有checkPropertyAndAssignValue
的承诺。避免使用反模式也有助于避免此错误:
verifyObject(complexObject) {
const result = {};
const propertiesEnum = ['fruits','vegetables','milk'];
if (!complexObject) {
return Promise.resolve({ result: undefined });
}
return this.checkPropertyAndAssignValue(complexObject,result)
.then(() => {
if (!Object.keys(result).length) {
console.log('resolve with undefined');
return { result: undefined };
}
console.log('resolve good');
return { result };
})
.catch((err) => {
console.log('enter error');
throw { message: err }; // *** Will get caught by the promise mechanism and turned into rejection
});
}
作为替代:如果您正在为现代环境编写此代码,则可能会发现async
函数和await
更加熟悉,因为它们使用相同的结构(throw
,try
,catch
),您习惯使用同步代码。例如:
async verifyObject(complexObject) {
const result = {};
const propertiesEnum = ['fruits','milk'];
if (!complexObject) {
return { result: undefined };
}
try {
await this.checkPropertyAndAssignValue(complexObject,result);
// ^^^^^−−−−− waits for the promise to settle
if (!Object.keys(result).length) {
console.log('return undefined');
return { result: undefined };
}
console.log('return good');
return { result };
} catch (err) {
console.log('enter error');
throw { message: err }; // *** FWIW,suggest making all rejections Error instances
// (even when using promises directly)
}
}
private async checkPropertyAndAssignValue(complexObject,result) {
// *** Note: This used to return a promise but didn't seem to have any asynchronous
// code in it. I've made it an `async` function,so if it's using something
// that returns a promise that you haven't shown,include `await` when getting
// its result.
for (const property of complexObject) {
if(complexObject[property] && Object.keys(complexObject[property]).length)
if(property === 'milk' && this.verifyMilk(complexObject[property]) === false) {
throw 'incomplete'; // *** FWIW,suggest making all rejections Error instances
// (even when using promises directly)
}
Object.assign(result,{[property]: complexObject[property]})
console.log('result is...:>',result);
}
console.log('final result:>',result);
return result;
}
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