String compression in JavaScript

I'm looking for a JavaScript function that given a string returns a compressed (shorter) string.

I'm developing a Chrome web application that saves long strings (HTML) to a local database. For testing purposes I tried to zip the file storing the database, and it shrank by a factor of five, so I figured it would help keep the database smaller if I compressed the things it stores.

I've found an implementation of LZSS in JavaScript here: http://code.google.com/p/u-lzss/ ("U-LZSS").

It seemed to work when I tested it "by hand" with short example strings (decode === encode), and it's reasonably fast too, in Chrome. But when given big strings (100 ko) it seems to garble/mix up the last half of the string.

Is it possible that U-LZSS expects short strings and can't deal with larger strings? And would it be possible to adjust some parameters in order to move that upper limit?

At Piskvor's suggestion, I tested the code found in an answer to this question: JavaScript implementation of Gzip (top-voted answer: LZW implementation) and found that:

1. it works
2. it reduces the size of the database by a factor of two

... which is less than 5 but better than nothing! So I used that.

(I wish I could have accepted an answer by Piskvor but it was only a comment).