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I've taken a look at a few questions on recursion in promises and am confused on how to implement them properly:

I put together a simple example (see below) - this is just an example so I can understand how to make recursion with promises work and not a representation of the code in which I'm working.

Net-net, I'd like the promise to resolve, but according to the output on node, it doesn't resolve. Any insight into how to make this resolve?

var i = 0;
var countToTen = function() { 
    return new Promise(function(resolve, reject) {
        if (i < 10) {
            console.log("i is now: " + i);
            return countToTen();
        else {
            resolve(i);
countToTen().then(console.log("i ended up at: " + i));
And the output on the console:
> countToTen().then(console.log("i ended up at: " + i));
i is now: 1
i is now: 2
i is now: 3
i is now: 4
i is now: 5
i is now: 6
i is now: 7
i is now: 8
i is now: 9
i is now: 10
i ended up at: 10
Promise { <pending> }
The promise never resolves.
                change return countToTen(); to resolve(countToTen()); - the console will still say "pending", however, if you instead say var p = countToten...... then you'll see p is resolved
– Jaromanda X
                Mar 27, 2018 at 23:34
                the other issue you have is that your .then is wrong ... .then expects a function as an argument, you have supplied undefined (the result of running console.log as an argument - which is why the output to the console looked OK to you
– Jaromanda X
                Mar 27, 2018 at 23:35
                Thank you @Jaromanda X, upvoted since you didn't write an answer, otherwise would have accepted yours.  Appreciate the response.
– joelc
                Mar 27, 2018 at 23:43
If you look at your code as long as i is less than 10 you are recursing and never resolving the promise. You eventually resolve a promise. but it is not the promise the initial caller gets. 
You need to resolve with the promise returned by the recursion. How the system works if you resolve with a promise it will still not resolve until also the value is resolved:
let i = 0;
const countToTen = () => new Promise((resolve, reject) => {
    if (i < 10) {
      console.log("i is now: " + i);
      resolve(countToTen());
    } else {
      resolve(i);
countToTen().then(() => console.log("i ended up at: " + i));
                you may want to also point out the incorrect usage of .then - since you changed that code too in your answer :p - because if .then was used correctly, OP would not have seen that final output
– Jaromanda X
                Mar 27, 2018 at 23:39
                Thanks  alot it really hepled me ! i was going to ask a new question .... Just in time found this answer :-) really happy .....
– Sanmeet
                Dec 13, 2021 at 15:52
  new Promise ((resolve, _) =>
    from < to
      ? (console.log (from), resolve (countTo (to, from + 1)))
      : resolve (from))
countTo (7, 2) .then (console.log, console.error)
// 2 3 4 5 6 7
const asyncUnfold = async (f, init) =>
  f ( async (x, acc) => [ x, ...await asyncUnfold (f, acc) ]
    , async () => []
    , init
const delay = (x, ms = 50) =>
  new Promise (r => setTimeout (r, ms, x))
const countTo = (to, from = 0) =>
  asyncUnfold
    ( async (next, done, acc) =>
        acc <= to
          ? next (await delay (acc), await delay (acc + 1))
          : done ()
    , from
countTo (10) .then (console.log, console.error)
// [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ]
countTo (7, 2) .then (console.log, console.error)
// [ 2, 3, 4, 5, 6, 7 ]
Here's a more practical example where we have a database of records and we wish to perform a recursive look-up, or something...
db.getChildren accepts a node id and returns only the node's immediate children
traverse accepts a node id and it recursively fetches all descendant children (in depth-first order)
const data =
  { 0 : [ 1, 2, 3 ]
  , 1 : [ 11, 12, 13 ]
  , 2 : [ 21, 22, 23 ]
  , 3 : [ 31, 32, 33 ]
  , 11 : [ 111, 112, 113 ]
  , 33 : [ 333 ]
  , 333 : [ 3333 ]
const db =
  { getChildren : (id) =>
      delay (data [id] || [])
const Empty =
  Symbol ()
const traverse = (id) =>
  asyncUnfold
    ( async (next, done, [ id = Empty, ...rest ]) =>
        id === Empty
          ? done ()
          : next (id, [ ...await db.getChildren (id), ...rest ])
    , [ id ]
traverse (0) .then (console.log, console.error)
// [ 0, 1, 11, 111, 112, 113, 12, 13, 2, 21, 22, 23, 3, 31, 32, 33, 333, 3333 ]
                Thanks.  It was just an example.  "I put together a simple example (see below) - this is just an example so I can understand how to make recursion with promises work and not a representation of the code in which I'm working."
– joelc
                Mar 28, 2018 at 15:00
Many members already mentioned, need to resolve with the promise returned by the recursion.
I would like to share code into async/await syntax.
const printNumber = (i) => console.log("i is now: " + i);
// recursive function to call number increment order
const recursiveCallNumber = async (i, checkCondition) => {
    // if false return it, other wise continue to next step
    if (!checkCondition(i)) return;
    // then print
    printNumber(i); 
     // then call again for print next number
    recursiveCallNumber(++i, checkCondition);
await recursiveCallNumber(1, (i) => i <= 10);
        
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