gistfile1.js

// deferred example from https://github.com/cujojs/when/blob/master/docs/api.md#nodefncreatecallback
var when, nodefn;

when   = require("when");
nodefn = require("when/node/function");

function nodeStyleAsyncFunction(callback) {
    if(Math.random() * 2 > 1) {
      callback("Oh no!");
    } else {
      callback(null, "Interesting value");
    }
}

var deferred = when.defer();
nodeStyleAsyncFunction(nodefn.createCallback(deferred.resolver));

deferred.promise.then(function(interestingValue) {
  console.log(interestingValue)
},function(err) {
  console.error(err)
});

gistfile2.js

// using DOM Promise constructor with resolver interface


function nodeStyleAsyncFunction(callback) {
  if (Math.random() * 2 > 1) {
    callback(new Error('Oh no!'))
  } else {
    callback(null, 'Interesting value')
  }
}

new Promise(function (resolve, reject) {
  nodeStyleAsyncFunction(function (err, val) {
    if (err) {
      reject(err)
    } else {
      resolve(val)
    }
  })
}).then(function (interestingValue) {
  console.log(interestingValue)
}, function (err) {
  console.error(err)
})

gistfile3.js

// generic node promise wrapper using DOM Promise constructor

function nodeStyleAsyncFunction(callback) {
  if (Math.random() * 2 > 1) {
    callback(new Error('Oh no!'))
  } else {
    callback(null, 'Interesting value')
  }
}

function wrap(fn) {
  return function () {
    var args = Array.prototype.slice.call(arguments)
    return new Promise(function (resolve, reject) {
      var callback = function (err, val) {
        if (err) {
          reject(err)
        } else {
          resolve(val)
        }
      }
      try {
        fn.apply(null, args.concat(callback))
      } catch (e) {
        reject(e)
      }
    })
    
  }
}

var regularAsyncFunction = wrap(nodeStyleAsyncFunction)

regularAsyncFunction().then(function (val) {
  console.log(val)
}, function (err) {
  console.error(err)
})