.then() function is called before main function gets completed - Q.nfcall - node.js

Question

A() function return promises after 1000 ms and throws an error. So, the next execution should be into catch. But, .then() function gets executed even after the main function throws an error.
Test.js
var Test1 = require("./Test1.js")
var Q = require('q');
var value = "Hardik";
var value1 = "Shah";
A()
.then(Test1.B(value, value1))
.catch(function(e){
console.log("In catch: ", e.message);
});
function A(){
console.log("In A function");
return Q.nfcall(AInner);
}
function AInner(callback){
setTimeout(function() {
callback({message: "Error from A Inner"});
}, 1000)
}
Test1.js
'use strict';
var Q = require("q");
module.exports = {B:B}
function B(value, value1){
console.log("In B function: ", value, " ", value1);
return Q.nfcall(BInner);
}
function BInner(callback){
console.log("In BInner function");
callback({message: "Error from BInner"});
}
Actual Output:
In A function
In B function: Hardik Shah
In BInner function
In catch: Error from A Inner
Expected Output:
In A function
Error from A Inner // After 1000 ms
I have solved issue by modifying below code: Works perfect
A()
.then(function(){
return Test1.B(value, value1)
}).then(function(data){
console.log("final data", data);
})
.catch(function(e){
console.log(e.message);
});
But, what is wrong with the above code?
Please give me a good explanation with the correct way to write code in the sequence of then rather than under then.
You can try here https://repl.it/#hrdk108/Hardik-Shah-Issue1 to reproduce an issue.

Answer 1

Issue is, you are invoking Test1.B(value, value1) inside then, rather than keeping it as callback. Because, once you used it as invocation, it started it's own promise chain. To fix it, change it to:
var Test1 = require("./Test1.js")
var Q = require('q');
var value = "Hardik";
var value1 = "Shah";
A()
.then(function() { Test1.B(value, value1) }) // note here
.catch(function(e){
console.log("In catch: ", e.message);
});
function A(){
console.log("In A function");
return Q.nfcall(AInner);
}
function AInner(callback){
setTimeout(function() {
callback({message: "Error from A Inner"});
}, 1000)
}

Answer 2

After a long brainstorm, I have figured out and it is just a silly mistake.
That Mistake is just because I invoked Test1.B() while defining
into then. Which is already answered in the above answer. So, One solution is I have already mentioned in the question.
Second solution:
The correct way to write a then sequence is:
Test1.B function without arguments:
A()
.then(Test1.B)
.catch(function(e){
console.log("In catch: ", e.message);
});
Test1.B with arguments: use bind
A()
.then(Test1.B.bind(null, value, value1))
.catch(function(e){
console.log("In catch: ", e.message);
});
Check here corrected example https://repl.it/#hrdk108/Hardik-Shah-Issue1
For Just FYI,
Actually, When you are using Q.nfcall you should take care of passing arguments design.
nfcall expects arguments provided individually
For Example:
Q.nfcall(B, value, value1);