Add `javascript-v.txt`

[mathiasbynens]

Once both https://github.com/tc39/proposal-regexp-set-notation AND #7 happen, we should export javascript-v.txt, a JavaScript-compatible regular expression pattern matching all the emoji in index.txt, for use in regular expressions with the v flag.

This pattern could be more concise than the u pattern, but would still require programmatically generated character class ranges.

• For each browser+version shipping support for the v flag, we’d note down the version of the Unicode/Emoji standard its data corresponds to. (The caniunicode project might be useful here.)
• Among all those browsers, we’d look at the lowest common denominator, i.e. the oldest possible Emoji standard version that is supported. We can then rely on all browsers supporting at least that Emoji version, so we only need to programmatically generate a pattern that matches the remaining emoji.
• We then combine that generated pattern with \p{Emoji_Test} (or whatever #7 ends up looking like).

The final pattern looks like this:

\p{Emoji_Test}|other|emoji|here

[mathiasbynens]

Once both https://github.com/tc39/proposal-regexp-set-notation AND #7 happen

Before that, once only https://github.com/tc39/proposal-regexp-set-notation happens, we can already provide a more optimal output flavor, since we could then rely on \p{RGI_Emoji} being supported in browsers, and thus subtract RGI_Emoji from the set of sequences we need to generate a pattern for. The pattern would look something like this:

\p{RGI_Emoji}|other|emoji|here

We could even make use of \q{other|emoji|here} if that ends up saving bytes compared to the current character class-based pattern.

Similarly to the above, we’d need to look at the oldest possible Emoji standard supported across all browsers that support the v flag.

[mathiasbynens]

javascript-v is now a build target. The only way to simplify this further is to standardize a new Unicode property of strings that exposes the emoji-test.txt data, as described in the top post. I’ll leave the issue open to track that.