Rails 3.1 Possible Bug in Asset Pipeline and Uglifier

You will probably find that one of you js files has a syntax error somewhere. This could be a missing semicolon at the end of a block, or some other minor problem. Often browsers will still load the js and it will work, but uglifier cannot compress it with those errors. I would start looking in the localisation files first.

One way to find out which file contains the error is to re precompile locally with a minimal set of files and add things one by one until it breaks. If it is due to a missing semicolon, the breakage will the second-last file you added.

Mine precompiled after I removed a stray "debugger" statement. Woops.

If anyone reading this thread encounters issues with unicode characters or "invalid byte sequence in UTF-8" in your rails app, try putting this in your production.rb file:

# override default uglifier options so we don't mangle unicode  config.assets.js_compressor = Uglifier.new(output: {ascii_only: true})

In my case, the uglifier was converting strings in my javascript like \udbff into UTF-8 characters í¯¿ which ultimately was breaking some unicode regex. (This was happening with turbo-sprockets and codemirror but you might encounter it anytime your javascript relies on ASCII representations of unicode characters.)