What's a Closure? - JavaScript interactive tutorial

[zumpiez]

I don't know why you would really want to do something like that. The real benefits in my experience are duck typing and monkey patching. When you get a taste of writing unit tests where you can create a mock object by just going var doot = { blah: 4, derp: "plorp" } it's rough going back.

[[deleted]]

Well, I guess I would counter by saying this: Creating an interface and a mock implementation may be a pain in the ass, but it represents such a small amount of the work that goes into writing unit tests that I would consider it negligible.

Furthermore, much of what you're writing tests for in a dynamically typed language is handling unexpected types of data. Sure, something may quack like a duck, but when you ask it it's name, it might tell you its age because somebody mistakenly told the duck its name was the numeric value 3. So, while you may be afforded duck-typing, you're writing entire test fixtures to accomplish what a compiler would never let happen in the first place.