In the spec, perhaps change "primes" to "digits" in "every four consecutive primes".

Thanks for this kata!

It'd be good to mention in the spec that discrete hour hand movement is required - snapping to each hour position. I appreciate that this can be inferred from the examples, anyway. Thanks for the kata!

Nice, thanks!

It's interesting that this has to wait until the very end of the input to detect a mismatched closing brace, e.g. "[)......", "())...." or even just "]......".

Of course, there's nothing against this in the spec. In fact this is perhaps the elegance of the solution: "We'll stack whatever, but if the stack hasn't been cleared via legitimate matches by the time we reach the end, we know we had a mismatch."

This would only be a problem with a very long-running (or infinite) input stream, where we might want to detect those illegal sequences immediately they occur: validBraces $ ']' : cycle "(())"

(Just musing as I learn, thanks!)

It'll take only the first match, from the top down. So, yes, you'd have problems if you reversed these two lines, but none as it stands.

Nice!

Minor point: \w matches digits and underscore, too, however, so 1000000 becomes abbreviated to 150, and one_two gets abbreviated where it should not, for example.

The \w in the regex here matches too much. In addition to alphabet characters, it also matches digits and the underscore character, '_'.

\w is equivalent to [A-Za-z0-9_]

As a result, this solution will abbreviate some inputs incorrectly.

For example:

• 1000000 will become 150 where it should be left untouched.
• snake_case will become s8e where it should be s3e_c2e
• left4dead will become l7d where it should be l2t4d2d
• abc_ will be abbreviated to a2_ where it should be left untouched.
• The_300 will be abbreviated to T50 where it should be left untouched.

This solution does currently (21/7/2016) pass the submission tests, however!

Here's documentation on \w for those who're curious: https://developer.mozilla.org/en/docs/Web/JavaScript/Guide/Regular_Expressions#special-word