Introduction to JavaScript source maps (opens in new tab)

There are a couple of existing forks / patches / pull requests with preliminary support for it. Given that its presence in Chromium means it'll probably land in Chrome proper in the next couple of months, we should try to merge and finish support for source maps before then.

Having to go to the trouble of understanding and implementing Base64 VLQ (since basically nobody uses it) myself just to prototype a source map implementation for my compiler makes me less likely to actually get around to it, because it's one more complete unknown in a format that seems to have almost nothing resembling working deployments or documentation to speak of.

It really sucks that the best source of information on 'how to create source maps' is the closure compiler source and not an actual spec or documentation (I searched around and the closest thing to docs I could find was an extremely concise Google Doc with gaps in it that may not match what is deployed in Chrome [1]). Being told 'just do what these guys do' is not a great way to get a new standard implemented on the web, especially when 'these guys' is Chrome Canary talking to a Google compiler.

Has anyone run across better documentation that clearly describes the file format, or a second implementation I can use to check that my source maps are correct? The only other choice I've run across is a (seemingly dead) Firefox 3.x addon that adds support for some reason of the source map format, specifically for supporting Closure Compiler. [2]

[1]: https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiO...

[2]: https://developers.google.com/closure/compiler/docs/inspecto...

To answer my own question, VLQ coding is used in other debugging symbol formats for the same reason.