根据Promise.all中的数据执行其他功能？

Question

Execute different function in Promise.all

Hi I'm new to javascript. I need to fetch data from different server which are dependent on each other. I want to execute different function depending on promise.

let us suppose I have fetched user data:

 let p1 = SomeApi.fetchUser();
 on successfull I want to execute function A


 let p2 = SomeApi.fetchStudent()
 on successfull I want to execute function B

let p3 = SomeApi.fetchSomething()
on successfull I want to execute function C

 How to achieve some thing like this

 Promise.all([p1, p2, p3]).then(data => {
  if(p1) {
    A()
  }
  if (p2){
    B()
  }
  if (p3) {
    C()
  }
 })

Assume all data are dependent on each other .

Answer 1

It sounds like you just need to call .then on the existing Promises. If you need a different action to take place once all Promises have resolved, then use Promise.all :

let p1 = SomeApi.fetchUser();
p1.then(a);
let p2 = SomeApi.fetchStudent()
p2.then(b);
let p3 = SomeApi.fetchSomething()
p3.then(c);

Promise.all([p1, p2, p3]).then(data => {
  // all Promises have resolved
})

If a , b , and c are completely synchronous and aren't expensive, you have them return the resolve value, and define each outer Promise to the chained call:

let p1 = SomeApi.fetchUser()
  .then(a);
let p2 = SomeApi.fetchStudent()
  .then(b);
let p3 = SomeApi.fetchSomething()
  .then(c);

Promise.all([p1, p2, p3]).then(data => {
  // all Promises have resolved
})

where a , b , and c are something like:

const a = (aData) => {
  // do something with aData
  return aData;
};

Returning the data at the end of the individual callback allows the Promise.all to use the resolve values from all Promises (if that's needed).

If there may be errors, then of course you should handle them as well with catch , eg:

let p1 = SomeApi.fetchUser();
p1.then(a).catch(handleErrors);
let p2 = SomeApi.fetchStudent()
p2.then(b).catch(handleErrors);
let p3 = SomeApi.fetchSomething()
p3.then(c).catch(handleErrors);

Promise.all([p1, p2, p3]).then(data => {
  // all Promises have resolved
}).catch(handleErrors)

Answer 2

You can add .then function to handler for dependent.

let p1 = SomeApi.fetchUser().then(()=>{
A();
return Promise.resolve()
});
 //on successfull I want to execute function A


 let p2 = SomeApi.fetchStudent().then(()=>{
B();
return Promise.resolve()
});
 //on successfull I want to execute function B

let p3 = SomeApi.fetchSomething().then(()=>{
C();
return Promise.resolve()
});
//on successfull I want to execute function C

 How to achieve some thing like this

 Promise.all([p1, p2, p3]).then(data => {
  if(data[0]) {

  }
  if (data[1]){

  }
  if (data[2]) {

  }
 });