Using Javascript in flash

I don't have examples for the first, but I guess you mean talking to javascript in the browser...I'm sure others who know about that will share ideas about what and why.

For the .jsfl flash javascript...its for scripting the Flash Authoring tool. To extend functionality or avoid repetitive tasks. I have one command extension for example that takes a drawing done in the authoring tool on stage and converts it to actionscript drawing commands. So it only works with the flash authoring tool... I did a quick google search there's a portion of this page with a code example:
http://www.twelvestone.com/forum_thread/view/31745