String compression in JavaScript

Question

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?

Answer 1

I just released a small LZW implementation especially tailored for this very purpose as none of the existing implementations did meet my needs.

• Here is the home page of the project

• Here is a link to a demo comparing it with LZMA level 1

That's what I'm using going forward, and I will probably try to improve the library at some point.

Answer 2

Here are encode (276 bytes, function en) and decode (191 bytes, function de) functions I modded from LZW in a fully working demo. There is no smaller or faster routine available on the internet than what I am giving you here.

function en(c){var x='charCodeAt',b,e={},f=c.split(""),d=[],a=f[0],g=256;for(b=1;b<f.length;b++)c=f[b],null!=e[a+c]?a+=c:(d.push(1<a.length?e[a]:a[x](0)),e[a+c]=g,g++,a=c);d.push(1<a.length?e[a]:a[x](0));for(b=0;b<d.length;b++)d[b]=String.fromCharCode(d[b]);return d.join("")}    function de(b){var a,e={},d=b.split(""),c=f=d[0],g=[c],h=o=256;for(b=1;b<d.length;b++)a=d[b].charCodeAt(0),a=h>a?d[b]:e[a]?e[a]:f+c,g.push(a),c=a.charAt(0),e[o]=f+c,o++,f=a;return g.join("")}    var compressed=en("http://www.ScriptCompress.com - Simple Packer/Minify/Compress JavaScript Minify, Fixify & Prettify 75 JS Obfuscators In 1 App 25 JS Compressors (Gzip, Bzip, LZMA, etc) PHP, HTML & JS Packers In 1 App PHP Source Code Packers Text Packer HTML Packer or v2 or v3 or LZW Twitter Compress or More Words DNA & Base64 Packer (freq tool) or v2 JS JavaScript Code Golfer Encode Between Quotes Decode Almost Anything Password Protect Scripts HTML Minifier v2 or Encoder or Escaper CSS Minifier or Compressor v2 SVG Image Shrinker HTML To: SVG or SVGZ (Gzipped) HTML To: PNG or v2 2015 JS Packer v2 v3 Embedded File Generator Extreme Packer or version 2 Our Blog DemoScene JS Packer Basic JS Packer or New Version Asciify JavaScript Escape JavaScript Characters UnPacker Packed JS JavaScript Minify/Uglify Text Splitter/Chunker Twitter, Use More Characters Base64 Drag 'n Drop Redirect URL DataURI Get Words Repeated LZMA Archiver ZIP Read/Extract/Make BEAUTIFIER & CODE FIXER WHAK-A-SCRIPT JAVASCRIPT MANGLER 30 STRING ENCODERS CONVERTERS, ENCRYPTION & ENCODERS 43 Byte 1px GIF Generator Steganography PNG Generator WEB APPS VIA DATAURL OLD VERSION OF WHAK PAKr Fun Text Encrypt Our Google");  var decompressed=de(compressed);    document.writeln('<hr>'+compressed+'<hr><h1>'+compressed.length+' characters versus original '+decompressed.length+' characters.</h1><hr>'+decompressed+'<hr>');