UPDATE: parts of this are out-of-date with the introduction of lazy evaluation in lodash.
these are the slides i used for a lightning talk at an austinjs meetup.
if you'd like to play around with some of the es6 features described in the talk, you can try out gunderscore, which is an example of what it would look like to write a generator-based underscore.
i ended up making a blog post out of this, and learned a lot about the state of the implementations in relation to the spec in the process.