Chain promises with then()

I'm using the when promise library to lift() my node style callbacks and promisify them...

var nodefn = require('when/node');

var one = nodefn.lift(oneFn),
    two = nodefn.lift(twoFn),
    three = nodefn.lift(threeFn);


function oneFn(callback){
    console.log('one');
    callback(null);
}

function twoFn(callback){
    console.log('two');
    callback(null);
}

function threeFn(callback){
    console.log('three');
    callback(null);
}

I want to call the functions in a chain, like this:

one().then(two).then(three).done();

But it gives me an error when calling the second callback function:

Uncaught TypeError: undefined is not a function

The error refers to the callback function within twoFn(callback).

What is the correct way to chain these functions together and execute one after the other?

The problem is that nodefn.lift doesn't know how many parameters the function has (zero), so it just takes the appearing arguments and appends its callback to them. In a then chain every callback receives the result of the previous promise (in your case: undefined), so your twofn will be called with two arguments: undefined and the nodeback.

So if you fix their arities, it should work:

Function.prototype.ofArity = function(n) {
    var fn = this, slice = Array.prototype.slice;
    return function() {
        return fn.apply(null, slice.call(arguments, 0, n));
    };
};
var one = nodefn.lift(oneFn).ofArity(0),
    two = nodefn.lift(twoFn).ofArity(0),
    three = nodefn.lift(threeFn).ofArity(0);