Welcome back to Emacs Rocks

Today we're taking a look at the glorious stuff to be done with swank-js

It's a REPL for JavaScript

I found it a little hard to install,

and I've added some convenient functions to set it up for myself.

but now I can jack into the JavaScript REPL

It has autocompletion, which is nice

But I can also run JavaScript straight from the buffer.

Eval is C-x C-e like in elisp

and the results are at the bottom

Let's square these numbers.

And I can eval-and-replace

That's pretty sweet

Okay, now for the awesome part ...

I made a little bouncy ball in Canvas

I am now connecting to it,

and I can do stuff with the browser from the REPL

But check it out -

I can write code straight in my editor too

Like setting the vertical and horizontal speed of the ball.

Both at the same time, please ... yeah!

Or I can change the elasticity of the ball,

to the point where it's gaining speed as it's bouncing.

whoa! - come back here!

Okay, let's check out the CSS

what about a nice red background?

nah ..

some stars then

yeah! cool

Now, time for some fun ...

Change the opacity, I'll make a new ball every time,

and then loop the anim 200 times.

See? There's the bouncy pattern.

Now we can change the entry speed ...

or the bounciness ...

This should dampen it quickly.

And this should make for some serious bouncing.

I can even change the gravity.

Okay, back to real animation

See, there's the pattern we just made

That's it for Emacs Rocks this time around

Swank-js is some pretty awesome stuff

If you can get it up and running that is

Till next time!