While loop using bluebird promises

Question

I am trying to implement a while loop using promises.

The method outlined here seems to work. http://blog.victorquinn.com/javascript-promise-while-loop it uses a fun

Answer 1

I prefer this implementation as its easier to simulate break and continue with it:

var Continue = {}; // empty object serves as unique value
var again = _ => Continue;

var repeat = fn => Promise.try(fn, again)
  .then(val => val === Continue && repeat(fn) || val);

Example 1: stops when either the source or the destination indicate an error

repeat(again => 
    source.read()
    .then(data => destination.write(data))
    .then(again)

Example 2: stop randomly if the coin flip given 90% probability results with a 0

var blah = repeat(again =>
    Promise.delay(1000)
    .then(_ => console.log("Hello"))
    .then(_ => flipCoin(0.9) && again() || "blah"));

Example 3: Loop with condition that returns the sum:

repeat(again => {
  if (sum < 100) 
    return fetchValue()
      .then(val => sum += val)
      .then(again));
  else return sum;
})