Re-factor ANSI color handling

[mgeier]

This is based on a PR I made for nbconvert: jupyter/nbconvert#225.

It also contains the "upgrade" to 16 ANSI colors from a future PR, see jupyter/nbconvert#245 and jupyter/nbconvert#259.

I've not yet updated the tests because I'd like to get some general feedback before.

WARNINGS:

• I'm new to JavaScript, this is my first non-trivial use of it. Please tell me anything that can be improved or made more idiomatic.
• I don't know if this has any performance implications
• The implementation uses some ES6 features, I hope there is some kind of transpiler involved to make this work on older browsers

[mgeier]

When I'm running the tests, I'm getting this (the same happens at Travis CI):

Page Error
  Message:   SyntaxError: Parse error
  Call stack:
Page Error
  Message:   SyntaxError: Parse error
  Call stack:

Does that mean that ES6 is not supported?
Or is it some other problem?

[minrk]

@mgeier ES6 isn't used in the notebook js yet, so you have to use ES5.

[mgeier]

@minrk OK, will do. What are the plans for ES6 support?

[minrk]

We are adding it in new projects in various places (JupyterLab, ipywidgets, etc.). I'm not sure if we will add ES6 support to the old notebook js, as it is planned to be replaced by the totally rewritten frontend code in JupyterLab, which is mostly using TypeScript and ES6.

[mgeier]

OK, thanks, that sounds reasonable.

I've re-based my initial commit (7bee6c5).

Then I've removed the ES6 stuff (245287a).
During that, I've also found out that conversion from a string to an integer number is insanely complicated in JavaScript and extended my code a bit. I hope now it's correct, but I've used another regex, so it might have become a bit slower.

Finally, I've updated the tests and added a new test case for overlapping formatting, which wasn't supported before (9d05258).
During that I found a little bug, so adding this test case already payed off.

Now Travis CI doesn't complain anymore, hooray!

I would love to hear some feedback about the new code!

What about the colors? Does everybody like them? Any suggestions for improvements?

[minrk]

No need to set length = 0 if we are returning here, plus length should be treated as read-only in general.

[mgeier]

I actually have to clear numbers here, because there might already be some entries from previous loop iterations.

Would you prefer if I used

numbers = [];

Or something entirely different?

[mgeier]

I just saw that there is an error because I'm not returning an Array in this case!

Would it be adequate to do this:

return [];

?

[mgeier]

... or should I rather use break;?

[mgeier]

As a different option, I tried to inline this function: db651f7 2bad374

Now the numbers Array is created only once, and never re-assigned.

What do you think about this?
If you don't like it, I can remove this commit again.

[mgeier]

@minrk Thanks for your comments, I've added a commit: 52fae53

[minrk]

Thanks!

[mgeier]

Thanks for merging!

[willingc]

Thanks @mgeier!

[KristofferC]

Thank you for this, looking forward to the new release.