Walk through implementing a Promises/A+ compliant promise from scratch — state machine, then-chaining, thenable assimilation, and why resolution must be asynchronous.

Imagine you ask your mom for a cookie, and she says 'I'll get it later.' That's like a Promise: it's a promise for something later. You can plan what to do when you get the cookie (or if you don't), and you can even tell your friend to do something with the cookie when it arrives.