How to start developing Javascript applications?

Question

I started developing Rails, but I soon realized that Rails without JS is pretty much useless. So, I'm trying to play with JS in my free time.

So what are trading tools (IDEs, if any) for JS development?

My main focus is on using APIs, Ajax, etc., so I don’t get lost when I get development of Rails applications that use JS.

There are many guides on using JS for the Open APIs or twitter APIs, but this should be done and abstractly some feature sets that a newbie should know.

In general, I begin to learn a language by making a calculator, from beginning to end (always works for me). But I can not make a calculator and use API / Ajax calls.

So what are your suggestions?

PS: I know about Douglas Crockford's video lectures, they are awesome, but I need something more specific.

UPDATE

My 2 source questions:
1. What are the trading tools for JS? Like Eclipse: Java :: X: Javascript, what is X (multiple Xs allowed)?
2. What example application do you recommend for me?

Answer 1

I think the most important thing: Know your language!

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@UPDATE

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Answer 2

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Answer 3

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});