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 (H

Answer 1

Try experimenting with textfiles before implementing anything because I think that the following does not necessarily hold:

so I figured it would help keep the database smaller if I compressed the things it stores.

That's because lossless compression algorithms are pretty good with repeating patterns (e.g whitespace).

Answer 2

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 3

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>');

Answer 4

It seems, there is a proposal of compression/decompression API: https://github.com/wicg/compression/blob/master/explainer.md .

And it is implemented in Chrome 80 (right now in Beta) according to a blog post at https://blog.chromium.org/2019/12/chrome-80-content-indexing-es-modules.html .

I am not sure I am doing a good conversion between streams and strings, but here is my try to use the new API:

function compress(string, encoding) {
  const byteArray = new TextEncoder().encode(string);
  const cs = new CompressionStream(encoding);
  const writer = cs.writable.getWriter();
  writer.write(byteArray);
  writer.close();
  return new Response(cs.readable).arrayBuffer();
}

function decompress(byteArray, encoding) {
  const cs = new DecompressionStream(encoding);
  const writer = cs.writable.getWriter();
  writer.write(byteArray);
  writer.close();
  return new Response(cs.readable).arrayBuffer().then(function (arrayBuffer) {
    return new TextDecoder().decode(arrayBuffer);
  });
}

const test = "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";

async function testCompression(text, encoding = 'deflate') {
  console.log(encoding + ':');
  console.time('compress');
  const compressedData = await compress(text, encoding);
  console.timeEnd('compress');
  console.log('compressed length:', compressedData.byteLength, 'bytes');
  console.time('decompress');
  const decompressedText = await decompress(compressedData, encoding);
  console.timeEnd('decompress');
  console.log('decompressed length:', decompressedText.length, 'characters');
  console.assert(text === decompressedText);
}

(async function () {
  await testCompression(test, 'deflate');
  await testCompression(test, 'gzip');
}());

Answer 5

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).

Answer 6

To me it doesn't seem reasonable to compress a string using UTF-8 as the destination... It looks like just looking for trouble. I think it would be better to lose some compression and using plain 7-bit ASCII as the destination.

In a toy 4 KB JavaScript demo I wrote for fun I used an encoding for the result of compression that stores four binary bytes into five chars chosen from a subset of ASCII of 85 chars that is clean for embedding in a JavaScript string (85^5 is slightly more than 8^4, but still fits in the precision of JavaScript integers). This makes compressed data safe for example for JSON without need of any escaping.