javascript promise while loop

promise-loop.js

'use strict';

// ref: http://blog.victorquinn.com/javascript-promise-while-loop

var q = require('bluebird');

var promiseWhile = function (condition, action) {
    var resolver = q.defer();

    var loop = function () {
        if (!condition()) {
            return resolver.resolve();
        }

        return q.cast(action())
            .then(loop)
            .catch(resolver.reject);
    };

    process.nextTick(loop);

    return resolver.promise;
};

// And below is a sample usage of this promiseWhile function
var sum = 0,
    stop = 10;

promiseWhile(function () {
    // Condition for stopping
    return sum < stop;
}, function () {
    var deffered = q.pending();

    setTimeout(function () {
        sum++;
        // Print out the sum thus far to show progress
        console.log(sum);
        deffered.resolve();
    }, 250);

    return deffered.promise;
}).then(function () {
    // Notice we can chain it because it's a Promise,
    // this will run after completion of the promiseWhile Promise!
    console.log("Done");
});