How to start developing Javascript apps?

Question

I started out with Rails development, but soon I realized Rails without JS is pretty much useless. So, I am trying to play with JS in my free time.

So, what are the "tools of trade (IDEs if any)" for JS development?

My primary focus is usage of APIs, Ajax etc, so that I don't get lost when I get develop Rails apps which uses JS.

There are many tutorials for using JS for Open graph API or twitter API, but that is to get things done and abstract some feature sets which a beginner should know.

I generally start learning a language by making a calculator, end to end (always works for me). But I cannot make a calculator and use API/Ajax calls.

So, what are your suggestions?

PS: I am aware about Douglas Crockford's video lectures, they are awesome, but I need some thing more concrete.

UPDATE:

My 2 original questions:
1. What are the tools of trade for JS? Like Eclipse:Java::X:Javascript, What is X (multiple Xs are allowed)?
2. What sample app do you recommend for me to start with?

Answer 1

I think the most important thing is: Know your language!

JavaScript libraries are useful, but if your do not know the language, you have no chance of getting something done that cannot be achieved using your library of choice. For example: JavaScript's prototype-system is very valuable and important for building robust applications. I really recommend that you experiment with this before diving into something you barely know. Closures are also very important to understand.

One thing is important, though: Do not spend too much time on browser incompatibilities. This is what most libraries are for. What you need to know is how the language works. Implementation-specific things are not worth learning (in most cases), since somebody already fixed those for you.

@PS: Douglas Crockford indeed does a pretty awesome job on explaining how JavaScript really works. You should keep watching this.

---

@UPDATE:

1. I think the X has it's origin in JavaScript's MIME-type: application/x-javascript. My tool of choice for web-development (including JavaScript) is NetBeans IDE. I use it in my workplace and it is very reliable and comfortable to work with. This is subjective (of course). Most other IDE's will do, too.
2. This is difficult to answer. I will update my post if something comes to my mind.