quickexample.js

const Promise = require("bluebird");
const fs = Promise.promisifyAll(require('fs'))

const getNumbers = () => new Promise((resolve, reject) => {
    var fileNumbers = [];
    for(var n = 0; n < 10; n++){
        fileNumbers.push(n);
    }
    resolve(fileNumbers);
});

Promise.all(getNumbers())
    .mapSeries((myNumbers) =>
        Promise.delay(3000).then(() => writeMyFile(myNumbers))
    );

var writeFileAsync = Promise.promisify(fs.writeFile, { context: fs });
function writeMyFile(fn){
    //I'm using writeFile here but Jimp uses writeFileStream and writes a buffer to it... 
    //the buffer doesn't return which is the same issue here
    return writeFileAsync("set\\" + fn + ".txt", "Hey there!")
        .then(() => console.log("The file was saved!"))
        .catch(err => console.log(err));
}