rsvp.js

I asked the same question in Twitter. Turns out James was actually augmenting (i.e. modifying) the array object `promises` to behave as a promise itself. I don't think this was a particularly beautiful way of doing it but it seems to work now that I think of it. Promise libraries, like RSVP.js [1] he referred to, typically implement a way to construct a promise with a depends-on-many relationship, as a function possibly called `all([p1, p2, ...])` (with the same type signature as for `list`), `and(p1, p2, ...)` or something similar. IMO, defining the `list` function that way would've been clearer to the reader and more FP'ish, treating the `promises` argument in as a value and not a mutable object. [1]: https://github.com/tildeio/rsvp.js/blob/master/lib/rsvp/all....

James does a good job of articulating why promises are such a useful abstraction, especially in JavaScript land. I've been working on a project recently that relies heavily on coordinating many asynchronously-populated values, and I don't even want to think about what the code would look like if we were wrangling callbacks manually. We actually extracted our promises implementation from the work we've been doing, and released it as RSVP.js[1]. While other JavaScript promises libraries are great, we specifically designed RSVP.js to be a lightweight primitive that can be embedded and used by other libraries. Effectively, it implements only what's needed to pass the Promises/A+ spec[2]. For a comparison of RSVP.js with other promises-based JavaScript asynchrony libraries, see this previous discussion on Hacker News[3]. 1: https://github.com/