Your mission: You are a Web 4.0 programmer from the future. For some reason we cannot possibly comprehend, you have come back to 2008 to impregnate your grandmother.
While you’re here it’s crucial to your mission that you also write a Web 2.0 app. Difficulty? Working in our ancient dialect of JavaScript. Solution? Mascara.
No, you don’t wear it, you use it.
Mascara is a program that translates tomorrow’s JavaScript into today’s JavaScript.
It’s been mentioned in some of the big JS venues like here and here, but I’ve been watching since and the author is really knocking the cover off the ball with new releases. I want to make sure he gets the attention he deserves.
Here’s the site:
And here’s the blog where you can read his changelist:
What’s This All About?
JavaScript moves slowly. Programmers are hesitant to use new features of the language until it shows up in all major browsers. You can’t just decide one day to move to the latest version. The version of JavaScript you have available depends on the browser that your client has installed.
Now, if you’re working on an Intranet, or on a Point-of-Sales system, you can mandate the browser. But for applications written for the web, you have to wait, and wait, and wait. Even after all that waiting, some people still haven’t managed to upgrade from IE6 yet. So you roll your eyes 
and wait some more.
One solution is to check to see if some language features are missing and provide them yourself (there are JavaScript libraries designed to help you out). That works fine when methods are missing, but it doesn’t work for new syntax.
What Mascara does it take future JavaScript (ECMAScript 4) and translate it into current JavaScript. It also does compile-time error checking.
Way to go We can all be future JavaScript programmers now.
Dreaming In JavaScript 