extend-promise.js

console.log(Q);
/*
 >> function Q(value) {
 >>   return resolve(value);
 >> }
 */

var promise = _.extend({
  "ref": function() {}
}, Q);

console.log(promise);
console.log(promise.ref);
/*
 * Expected:
 >> function Q(value) {
 >>   return resolve(value);
 >> }
 >>
 >> function() {}
 *
 * Actual:
 >> Object {ref: function, longStackJumpLimit: 1, nextTick: function, defer: function, promise: function…}
 >>
 >> function() {}
 */

/*
 * While I have your attention, while debugging this I noticed something else
 * fairly interesting: the new callback and thisArgs support in extend/assign,
 * and merge causes issues with source objects like Q that are also functions.
 */
var promise = _.extend({}, {
  "ref": function() {}
}, Q);

console.log(promise);
/*
 * Expected:
 >> function Q(value) {
 >>   return resolve(value);
 >> }
 *
 * Actual:
 >> Object {ref: makePromise}
 */

Your _.extend issue was addressed in c280347.

Having seen issue thread for lodash/lodash#184 in my email, I figured as much. Now that I've upgraded (back) to edge, the following code works:

var promise = _.extend(_.bind(Q), Q, {
  "ref": function() {}
});

Switching the order of the last two arguments does not work: I suppose because Lo-Dash has no way of determining if the function provided as the last argument (or second-to-last) is a callback or sourceN. I'm not sure how popular this is, though I believe it warrants a mention in the documentation.

The behavior of _.assign is mentioned in the docs, with the fix in edge the callback behavior will not be used if callback is the first or second arg.