Mixing
Create a Promise<Map> from several Promise
I am trying to get the bills for a number of customers, using typescript:
I have a Server class, handling the queries to the server, and providing a getBills class, which returns a Promise<Bill>:
class Server {
constructor(hostname?: string) {
hostname = hostname || "";
}
getBills(customer: Customer): Promise<Datapoint> {
const apiEndPoint = new URL("/API/Bills");
let parameters = { customer: customer.name};
//Fetch official doc
//https://github.com/whatwg/fetch/issues/56
Object.keys(parameters).forEach(key => apiEndPoint.searchParams.append(key, parameters[key]));
return fetch(apiEndPoint.toString())
.then(response => {
if (!response.ok) {
throw new Error(response.statusText)
}
return response.json()
})
}
}
I would like to query the bills for several customers, and return a Map for further processing (and to keep it all async, a Promise<Map<Customer, Bill>>, but I am struggling with this step.
What I have so far:
getBills(): Promise<Map<Customer, Bill>> {
let server = this.context.server;
let resultMap = new Map<Customer, Bill>();
let promises = ;
for (let customer of this.customers) {
promises.push(
server.getBills(customer).then(result => resultMap.set(customer, result))
);
}
Promise.all(promises).then(return resultMap);
}
But it does not compile, since it is trying to return the map itself, and not a Promise.
I have tried to use
Promise.all(promises).then(return Promise.resolve(resultMap));
but is does not work either.
Could you point me in the right direction?
typescript promise
asked Jan 2 at 10:59
MaximeMaxime
570415
add a comment |
I am trying to get the bills for a number of customers, using typescript:
I have a Server class, handling the queries to the server, and providing a getBills class, which returns a Promise<Bill>:
class Server {
constructor(hostname?: string) {
hostname = hostname || "";
}
getBills(customer: Customer): Promise<Datapoint> {
const apiEndPoint = new URL("/API/Bills");
let parameters = { customer: customer.name};
//Fetch official doc
//https://github.com/whatwg/fetch/issues/56
Object.keys(parameters).forEach(key => apiEndPoint.searchParams.append(key, parameters[key]));
return fetch(apiEndPoint.toString())
.then(response => {
if (!response.ok) {
throw new Error(response.statusText)
}
return response.json()
})
}
}
I would like to query the bills for several customers, and return a Map for further processing (and to keep it all async, a Promise<Map<Customer, Bill>>, but I am struggling with this step.
What I have so far:
getBills(): Promise<Map<Customer, Bill>> {
let server = this.context.server;
let resultMap = new Map<Customer, Bill>();
let promises = ;
for (let customer of this.customers) {
promises.push(
server.getBills(customer).then(result => resultMap.set(customer, result))
);
}
Promise.all(promises).then(return resultMap);
}
But it does not compile, since it is trying to return the map itself, and not a Promise.
I have tried to use
Promise.all(promises).then(return Promise.resolve(resultMap));
but is does not work either.
Could you point me in the right direction?
typescript promise
asked Jan 2 at 10:59
MaximeMaxime
570415
add a comment |
I am trying to get the bills for a number of customers, using typescript:
I have a Server class, handling the queries to the server, and providing a getBills class, which returns a Promise<Bill>:
class Server {
constructor(hostname?: string) {
hostname = hostname || "";
}
getBills(customer: Customer): Promise<Datapoint> {
const apiEndPoint = new URL("/API/Bills");
let parameters = { customer: customer.name};
//Fetch official doc
//https://github.com/whatwg/fetch/issues/56
Object.keys(parameters).forEach(key => apiEndPoint.searchParams.append(key, parameters[key]));
return fetch(apiEndPoint.toString())
.then(response => {
if (!response.ok) {
throw new Error(response.statusText)
}
return response.json()
})
}
}
I would like to query the bills for several customers, and return a Map for further processing (and to keep it all async, a Promise<Map<Customer, Bill>>, but I am struggling with this step.
What I have so far:
getBills(): Promise<Map<Customer, Bill>> {
let server = this.context.server;
let resultMap = new Map<Customer, Bill>();
let promises = ;
for (let customer of this.customers) {
promises.push(
server.getBills(customer).then(result => resultMap.set(customer, result))
);
}
Promise.all(promises).then(return resultMap);
}
But it does not compile, since it is trying to return the map itself, and not a Promise.
I have tried to use
Promise.all(promises).then(return Promise.resolve(resultMap));
but is does not work either.
Could you point me in the right direction?
typescript promise
asked Jan 2 at 10:59
MaximeMaxime
570415
I am trying to get the bills for a number of customers, using typescript:
I have a Server class, handling the queries to the server, and providing a getBills class, which returns a Promise<Bill>:
class Server {
constructor(hostname?: string) {
hostname = hostname || "";
}
getBills(customer: Customer): Promise<Datapoint> {
const apiEndPoint = new URL("/API/Bills");
let parameters = { customer: customer.name};
//Fetch official doc
//https://github.com/whatwg/fetch/issues/56
Object.keys(parameters).forEach(key => apiEndPoint.searchParams.append(key, parameters[key]));
return fetch(apiEndPoint.toString())
.then(response => {
if (!response.ok) {
throw new Error(response.statusText)
}
return response.json()
})
}
}
I would like to query the bills for several customers, and return a Map for further processing (and to keep it all async, a Promise<Map<Customer, Bill>>, but I am struggling with this step.
What I have so far:
getBills(): Promise<Map<Customer, Bill>> {
let server = this.context.server;
let resultMap = new Map<Customer, Bill>();
let promises = ;
for (let customer of this.customers) {
promises.push(
server.getBills(customer).then(result => resultMap.set(customer, result))
);
}
Promise.all(promises).then(return resultMap);
}
But it does not compile, since it is trying to return the map itself, and not a Promise.
I have tried to use
Promise.all(promises).then(return Promise.resolve(resultMap));
but is does not work either.
Could you point me in the right direction?
typescript promise
typescript promise
asked Jan 2 at 10:59
MaximeMaxime
570415
asked Jan 2 at 10:59
MaximeMaxime
570415
asked Jan 2 at 10:59
MaximeMaxime
570415
asked Jan 2 at 10:59
MaximeMaxime
570415
asked Jan 2 at 10:59
MaximeMaxime
570415
570415
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
It is a syntax error to write:
.then(return resultMap);
The then method must receive a function as argument, while return is just a statement, not a function. So change to:
.then(() => resultMap);
answered Jan 2 at 11:10
trincottrincot
129k1689123
add a comment |
@trincot already explained the syntax error, but instead of just writing return Promise.all(promises).then(() => { return resultMap; }); I would suggest not constructing the Map until you have all the results:
getBills(): Promise<Map<Customer, Bill>> {
const server = this.context.server;
const promises = this.customers.map(customer =>
server.getBills(customer).then(bills => [customer, bills])
);
return Promise.all(promises).then(tuples => new Map(tuples));
}
answered Jan 2 at 12:07
BergiBergi
378k63577908
Thank you for the suggestion, but I have trouble getting it to work. Indeed, as is,promisesis a nested array, with typePromise<(Customer | Bill)>I guess I would need to flatten this array, but doing this while keeping type safety seems more tedious than doing nothing :)
– Maxime
Jan 2 at 16:01
@Maxime the type interference can't know, but what I meant wasPromise<[Customer, Bill]>. UsingPromise.allon that gives us aPromise<[Customer, Bill]>where we have an array of tuples (not an array of arrays ofCumstomers orBills), which is exactly what theMapconstructor expects.
– Bergi
Jan 2 at 19:16
1
thank you for the explanation. The solution was to explicitely type the tuple:const promises = this.customers.map(customer => server.getBills(customer).then(bills => { return <[Customer, Bills]>[customer, bills]}))
– Maxime
Jan 3 at 7:59
add a comment |
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2 Answers
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active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
It is a syntax error to write:
.then(return resultMap);
The then method must receive a function as argument, while return is just a statement, not a function. So change to:
.then(() => resultMap);
answered Jan 2 at 11:10
trincottrincot
129k1689123
add a comment |
It is a syntax error to write:
.then(return resultMap);
The then method must receive a function as argument, while return is just a statement, not a function. So change to:
.then(() => resultMap);
answered Jan 2 at 11:10
trincottrincot
129k1689123
add a comment |
It is a syntax error to write:
.then(return resultMap);
The then method must receive a function as argument, while return is just a statement, not a function. So change to:
.then(() => resultMap);
answered Jan 2 at 11:10
trincottrincot
129k1689123
It is a syntax error to write:
.then(return resultMap);
The then method must receive a function as argument, while return is just a statement, not a function. So change to:
.then(() => resultMap);
answered Jan 2 at 11:10
trincottrincot
129k1689123
answered Jan 2 at 11:10
trincottrincot
129k1689123
answered Jan 2 at 11:10
trincottrincot
129k1689123
answered Jan 2 at 11:10
trincottrincot
129k1689123
129k1689123
add a comment |
add a comment |
@trincot already explained the syntax error, but instead of just writing return Promise.all(promises).then(() => { return resultMap; }); I would suggest not constructing the Map until you have all the results:
getBills(): Promise<Map<Customer, Bill>> {
const server = this.context.server;
const promises = this.customers.map(customer =>
server.getBills(customer).then(bills => [customer, bills])
);
return Promise.all(promises).then(tuples => new Map(tuples));
}
answered Jan 2 at 12:07
BergiBergi
378k63577908
Thank you for the suggestion, but I have trouble getting it to work. Indeed, as is,promisesis a nested array, with typePromise<(Customer | Bill)>I guess I would need to flatten this array, but doing this while keeping type safety seems more tedious than doing nothing :)
– Maxime
Jan 2 at 16:01
@Maxime the type interference can't know, but what I meant wasPromise<[Customer, Bill]>. UsingPromise.allon that gives us aPromise<[Customer, Bill]>where we have an array of tuples (not an array of arrays ofCumstomers orBills), which is exactly what theMapconstructor expects.
– Bergi
Jan 2 at 19:16
1
thank you for the explanation. The solution was to explicitely type the tuple:const promises = this.customers.map(customer => server.getBills(customer).then(bills => { return <[Customer, Bills]>[customer, bills]}))
– Maxime
Jan 3 at 7:59
add a comment |
@trincot already explained the syntax error, but instead of just writing return Promise.all(promises).then(() => { return resultMap; }); I would suggest not constructing the Map until you have all the results:
getBills(): Promise<Map<Customer, Bill>> {
const server = this.context.server;
const promises = this.customers.map(customer =>
server.getBills(customer).then(bills => [customer, bills])
);
return Promise.all(promises).then(tuples => new Map(tuples));
}
answered Jan 2 at 12:07
BergiBergi
378k63577908
Thank you for the suggestion, but I have trouble getting it to work. Indeed, as is,promisesis a nested array, with typePromise<(Customer | Bill)>I guess I would need to flatten this array, but doing this while keeping type safety seems more tedious than doing nothing :)
– Maxime
Jan 2 at 16:01
@Maxime the type interference can't know, but what I meant wasPromise<[Customer, Bill]>. UsingPromise.allon that gives us aPromise<[Customer, Bill]>where we have an array of tuples (not an array of arrays ofCumstomers orBills), which is exactly what theMapconstructor expects.
– Bergi
Jan 2 at 19:16
1
thank you for the explanation. The solution was to explicitely type the tuple:const promises = this.customers.map(customer => server.getBills(customer).then(bills => { return <[Customer, Bills]>[customer, bills]}))
– Maxime
Jan 3 at 7:59
add a comment |
@trincot already explained the syntax error, but instead of just writing return Promise.all(promises).then(() => { return resultMap; }); I would suggest not constructing the Map until you have all the results:
getBills(): Promise<Map<Customer, Bill>> {
const server = this.context.server;
const promises = this.customers.map(customer =>
server.getBills(customer).then(bills => [customer, bills])
);
return Promise.all(promises).then(tuples => new Map(tuples));
}
answered Jan 2 at 12:07
BergiBergi
378k63577908
@trincot already explained the syntax error, but instead of just writing return Promise.all(promises).then(() => { return resultMap; }); I would suggest not constructing the Map until you have all the results:
getBills(): Promise<Map<Customer, Bill>> {
const server = this.context.server;
const promises = this.customers.map(customer =>
server.getBills(customer).then(bills => [customer, bills])
);
return Promise.all(promises).then(tuples => new Map(tuples));
}
answered Jan 2 at 12:07
BergiBergi
378k63577908
answered Jan 2 at 12:07
BergiBergi
378k63577908
answered Jan 2 at 12:07
BergiBergi
378k63577908
answered Jan 2 at 12:07
BergiBergi
378k63577908
378k63577908
Thank you for the suggestion, but I have trouble getting it to work. Indeed, as is,promisesis a nested array, with typePromise<(Customer | Bill)>I guess I would need to flatten this array, but doing this while keeping type safety seems more tedious than doing nothing :)
– Maxime
Jan 2 at 16:01
@Maxime the type interference can't know, but what I meant wasPromise<[Customer, Bill]>. UsingPromise.allon that gives us aPromise<[Customer, Bill]>where we have an array of tuples (not an array of arrays ofCumstomers orBills), which is exactly what theMapconstructor expects.
– Bergi
Jan 2 at 19:16
1
thank you for the explanation. The solution was to explicitely type the tuple:const promises = this.customers.map(customer => server.getBills(customer).then(bills => { return <[Customer, Bills]>[customer, bills]}))
– Maxime
Jan 3 at 7:59
add a comment |
Thank you for the suggestion, but I have trouble getting it to work. Indeed, as is,promisesis a nested array, with typePromise<(Customer | Bill)>I guess I would need to flatten this array, but doing this while keeping type safety seems more tedious than doing nothing :)
– Maxime
Jan 2 at 16:01
@Maxime the type interference can't know, but what I meant wasPromise<[Customer, Bill]>. UsingPromise.allon that gives us aPromise<[Customer, Bill]>where we have an array of tuples (not an array of arrays ofCumstomers orBills), which is exactly what theMapconstructor expects.
– Bergi
Jan 2 at 19:16
1
thank you for the explanation. The solution was to explicitely type the tuple:const promises = this.customers.map(customer => server.getBills(customer).then(bills => { return <[Customer, Bills]>[customer, bills]}))
– Maxime
Jan 3 at 7:59
Thank you for the suggestion, but I have trouble getting it to work. Indeed, as is,
promises is a nested array, with type Promise<(Customer | Bill)> I guess I would need to flatten this array, but doing this while keeping type safety seems more tedious than doing nothing :)– Maxime
Jan 2 at 16:01
Thank you for the suggestion, but I have trouble getting it to work. Indeed, as is,
promises is a nested array, with type Promise<(Customer | Bill)> I guess I would need to flatten this array, but doing this while keeping type safety seems more tedious than doing nothing :)– Maxime
Jan 2 at 16:01
@Maxime the type interference can't know, but what I meant was
Promise<[Customer, Bill]>. Using Promise.all on that gives us a Promise<[Customer, Bill]> where we have an array of tuples (not an array of arrays of Cumstomers or Bills), which is exactly what the Map constructor expects.– Bergi
Jan 2 at 19:16
@Maxime the type interference can't know, but what I meant was
Promise<[Customer, Bill]>. Using Promise.all on that gives us a Promise<[Customer, Bill]> where we have an array of tuples (not an array of arrays of Cumstomers or Bills), which is exactly what the Map constructor expects.– Bergi
Jan 2 at 19:16
1
1
thank you for the explanation. The solution was to explicitely type the tuple:
const promises = this.customers.map(customer => server.getBills(customer).then(bills => { return <[Customer, Bills]>[customer, bills]}))– Maxime
Jan 3 at 7:59
thank you for the explanation. The solution was to explicitely type the tuple:
const promises = this.customers.map(customer => server.getBills(customer).then(bills => { return <[Customer, Bills]>[customer, bills]}))– Maxime
Jan 3 at 7:59
add a comment |
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