So something like:
UUUXXXXXXXXXXXXXXXXXXXXTTTTTKKKKKwould be encoded to:
3U20X5T5KIn this case, the encoded version of the text has been reduced by ~73%. But note that there may be cases where the encoded text would end up larger than the actual (decoded) plain text; this happens when the text contains many isolated characters rather than runs of characters.
Take for example abcdefghijklmnopqrstuvwxyz (26 characters); if you 'compress' that using a run-length algorithm, you'll end up with 1a1b1c1d1e1f1g1h1i1j1k1l1m1n1o1p1q1r1s1t1u1v1w1x1y1z (52 characters) which is a 100% increase from the decoded version.
Source and demoThe source can be found at https://github.com/dreasgrech/runlength-js
And the demo of the encoder is at http://dreasgrech.com/upload/runlength/
Note that as of current, the code does not handle instances where the decoded text contains digits.