[英]Call a Q promise function after promise chain invoked
I am working in a Node.js app with Q promise library. 我正在使用带有Q Promise库的Node.js应用程序。 I have two set of promise chains and one is for controlling the flow and one for calling service methods where I retrieve data from, My question is, I need to get the return value of the promise chain to my other promise chain. 我有两组承诺链,一组用于控制流程,另一组用于调用从中检索数据的服务方法。我的问题是,我需要将承诺链的返回值传递给我的其他承诺链。
MyExample.js MyExample.js
bookService.getBookById(bookId)
.then(bookDetals)
.then(function(returnValue) { // <- (A)
res.send(200, returnValue); // <- (C)
return returnValue;
}).catch(function(error) {
logger.error('Error getting values');
res.send(500, error);
});
bookDetals = function(book) {
myService.retrieveATypeData(book, bookId)
.then(function(bookData) {
myService.retrieveBTypeData(bookId)
.then(function(bdata) {
bookData[bTypeData] = bdata;
myService.retrieveCTypeData(bookId)
.then(function(cdata) {
bookData[cTypeData] = cdata;
}).done(function() {
return bookData; // <- (B)
})
});
});
};
In the above code, I am calling bookService.getBookById(bookId) and getting the book. 在上面的代码中,我正在调用bookService.getBookById(bookId)并获取书。 Then I am calling bookDetals function which is a promise chain. 然后我调用bookProtals函数,这是一个承诺链。 But my problem is it returns the returnValue before the promise chains over. 但是我的问题是,在诺言链结束之前,它会返回returnValue 。 How can I get the return value of promise chain (in line (B)) to return in place (C). 我如何获得承诺链的返回值(在行(B)中)以返回到位(C)。 Currently it return before. 目前它返回之前。 so in place C it says undefined. 因此,在C语言中,它表示未定义。
Since you are using Node, I would move towards ES6 Promises. 由于您正在使用Node,因此我将转向ES6 Promises。 If your current version does not yet support ES6 Promises, I would recommend you switch over to a library ( es6-promise ) that polyfills it for you. 如果您当前的版本尚不支持ES6 Promises,建议您切换到为您多填充的库( es6-promise )。 With ES6, you could do something like this: 使用ES6,您可以执行以下操作:
// mock async promise
const getThing = id => (
new Promise((resolve, reject) => {
setTimeout(() => {
resolve({
id
});
}, 250);
})
);
// mock async promise
const getDetailsA = thing => {
return new Promise((resolve, reject) => {
setTimeout(() => {
resolve(Object.assign({}, thing, {
a: 'purple'
}));
}, 250);
})
};
// mock async promise
const getDetailsB = thing => (
new Promise((resolve, reject) => {
setTimeout(() => {
resolve(Object.assign({}, thing, {
b: 'monkey'
}));
}, 250);
})
);
// mock async promise
const getDetailsC = thing => (
new Promise((resolve, reject) => {
setTimeout(() => {
resolve(Object.assign({}, thing, {
c: 'dishwasher'
}));
}, 250);
})
);
getThing('123')
.then(getDetailsA)
.then(getDetailsB)
.then(getDetailsC)
.then(console.log)
.catch(console.error);
You need to return a promise : 您需要返回一个承诺 :
bookDetals = function(book) {
return Q.Promise(function(resolve, reject, notify) {
myService.retrieveATypeData(book, bookId)
.then(function(bookData) {
myService.retrieveBTypeData(bookId)
.then(function(bdata) {
bookData[bTypeData] = bdata;
myService.retrieveCTypeData(bookId)
.then(function(cdata) {
bookData[cTypeData] = cdata;
}).done(function() {
resolve(bookData); // <- (B)
})
});
});
}
}
deferred is an anti-pattern discussed here . deferred是此处讨论的反模式。 Honestly, it might be best to use a polyfill since Promise is in the es6 spec. 老实说,它可能是最好使用填充工具 ,因为承诺是在ES6规范。
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