Add prefix string to error log

[tedyu]

This PR adds prefix string when error is encountered.

In elk, we sometimes saw the follwing:

 TypeError: removeMarkdown(...).substr is not a function

It might be possible that removeMarkdown wasn't able to parse the argument.

However, there is not much clue what error happened.

With the error prefix, it would be easier to find the cause.

[tedyu]

Alternatively we can throw the error.
To keep backward compatibility, we can add option (default to false) which allows the error to be thrown out.

[hongaar]

How would this change help you with triaging your issue?

Alternatively, could you add a breakpoint and step through the code (of remove-markdown) to pinpoint the line the error occurs in?

[tedyu]

@hongaar
I added an option, throwError (default false), to keep backward compatibility.

add a breakpoint and step through the code
Since the TypeError happened in production and we don't have the input that triggered the situation, currently we cannot debug this way.
Once the PR is accepted, we can upgrade to the next release and obtain the input for further debugging.

cc @zuchka

Thanks

[tedyu]

@zuchka
Can you take a look ?
Thanks

[tedyu]

Gentle ping, @zuchka

[stiang]

@tedyu I’m not really involved with this repo anymore, but if you are struggling to get your PR merged, I would suggest that you temporarily point your production setup to the fork with the PR in it (most dependency resolvers support pointing directly to a GitHub branch), figure out what caused the exception using your new option to throw errors, and then maybe switch back to the regular package. I see no reason to wait for this to get merged to figure out what is causing the bug, now that you already have a fork that can help.

[zuchka]

merged! so sorry for the delay

[zuchka]

shall we do some more testing before we cut a new release, @tedyu?

[tedyu]

This PR seems pretty safe.
Looking forward for the new release containing this PR.

Thanks

[zuchka]

I'll cut a new release in the next day or so 👍

[tedyu]

@zuchka
What's the release that contains this PR ?

Thanks