js_to_json() is swallowing commas in JS dicts at the end of a line when a line comment ending in } is following

[mhartkorn]

Make sure you are using the latest version: run youtube-dl --version and ensure your version is 2018.07.04. If it's not, read this FAQ entry and update. Issues with outdated version will be rejected.

• I've verified and I assure that I'm running youtube-dl 2018.07.04

Before submitting an issue make sure you have:

• At least skimmed through the README, most notably the FAQ and BUGS sections
• Searched the bugtracker for similar issues including closed ones
• Checked that provided video/audio/playlist URLs (if any) are alive and playable in a browser

What is the purpose of your issue?

• Bug report (encountered problems with youtube-dl)
• Site support request (request for adding support for a new site)
• Feature request (request for a new functionality)
• Question
• Other

---

Description of your issue, suggested solution and other information

As mentioned in PR #16317 by @dstftw js_to_json() has a bug that is removing commas (,) at line endings when a } inside a line comment is following. I debugged this a bit and got to the following minimal reproducible example.

Extracted JavaScript code from website:

{foo: 0, //}
bar : 1}

Result after putting it into js_to_json() (notice the space after 0):

{"foo": 0 
"bar" : 1}

When running it in a debugger, it turns out that fix_kv() (the callback inside js_to_json()) is receiving the , after 0 as a separate match and because of this condition it's removing the comma all together:

if v in ('true', 'false', 'null'):
    return v
elif v.startswith('/*') or v.startswith('//') or v == ',':
    return ""

I cannot fix this by myself because I'm not familiar enough with regex to make an adequate fix. I suspect that there should be a check added to see if the following } (which is apparently interpreted as the termination of the dict) is inside a comment (or the skip group alltogether?).