Callback Hell with Promises

Question

I got myself stuck in a pyramid of doom using Promises.

I have the following:

getA
getB
getC

getC depends on getB (and getA) that depends on getA.

So I must call them like this

getA(param)
  .then(getB)
  .then(getC)

but, as stated, I need the output of getA as a paramater to getC, so I did this

getA(param)
  .then(function (A) {
    getB(A)
      .then(function (B) {
        getC(A, B)
      });
  });

yes, the pyramid got me... I have brought shame upon my family. Help me regain my honor back.

score 0 · Answer 1 · answered Nov 22 '15 at 16:43

0

I think You can do like this.

var S;
getA(param)
.then(function (A) {
    return S = A;
})
.then(getB)
.then(function (B) {
    return getC(S, B);
})
.then(function (C) {
    console.log(C);
});

answered Nov 22 '15 at 16:43

sohan nohemy

615
5
13

score -1 · Answer 2 · answered Nov 22 '15 at 16:38

-1

You can use Promise.all to wait for multiple promises :

your pseudo code becomes :

var pa = new Promise(function(){/*function A*/});
var pb = new Promise(function(){
    pa.then(function {/*function B*/}
});
Promise.all([pa, pb]).then(function(){/*function C*/});

answered Nov 22 '15 at 16:38

Alice Oualouest

836
12
20

1

You need a `return` before `pa.then` or it won't work. Nice idea using Promise.all, but -1 for promise-constrictor anti-pattern. `getA` etc. already return promises, so there's zero need for constructors. – jib Nov 23 '15 at 00:50
Not to mention that you are using the Promise constructor incorrectly. Without calling `resolve` or `reject` the promise will never fulfill. – Nov 24 '15 at 09:12

Callback Hell with Promises

2 Answers2