promiseForPath - function for use with Q library

gistfile1.js

// Works like underscore-contrib's getPath function.
// Takes a promise that will resolve to an object and a dot notation string specifying a path.
//
// Cannot know if path exists in resolved value - returned promise will reject with a TypeError if you 
// specify a subkey of a nonexistent key, and undefined for a single
// nonexistent key.

function promiseForPath(promise, path) {
  var k = path.split('.');
  return k.reduce(function(memo, item){
    return memo.get(item);
  }, promise);
}