CODEWITHSUNDEEP
javascriptcompression
AgileMeansDoAsLittleAsPossible
AgileMeansDoAsLittleAsPossible

Reputation: 3617

Compressing plaintext in JavaScript?

I have a simple Notepad-like web application I'm making for fun. When you save a document, the contents of a <textarea> are sent to the server via Ajax and persisted in a database.

Let's just say for shits and giggles that we need to compress the contents of the <textarea> before sending it because we're on a 2800 baud modem.

Are there JavaScript libraries to do this? How well does plain text compress in the first place?

Upvotes: 1

Views: 4583

Answers (4)

Jstodd
Jstodd

Reputation: 1

It varies heavily on the algorithm and the text.

I'm making my own compression algorithm here, as of writing its not done but it already works extremely well for English plaintext compression. ~50% compression for both small and large messages. It wouldn't be useful to share a code snippet because I'm using experimental dictionary compression, but heres my project: https://github.com/j-stodd/SMOL

I also tried the LZW compression shared by Suirtimed but it doesn't seem to perform that well, it will decrease length but bytes stay mostly the same. Compressing "aaaaaaaa" with LZW will save you only one byte. My algorithm would save you 5 bytes.

Upvotes: 0

Demitrius Nelon
Demitrius Nelon

Reputation: 1248

Simple 7 bit compression might work if you're only using the 7 bit ascii character set. A google search yielded this: http://www.iamcal.com/png-store/

Or you could use LZW http://rosettacode.org/wiki/LZW_compression#JavaScript

As far as compression ratio; according to Dr. Dobbs:

It is somewhat difficult to characterize the results of any data compression technique. The level of compression achieved varies quite a bit, depending on several factors. LZW compression excels when confronted with data streams that have any type of repeated strings. Because of this, it does extremely well when compressing English text. Compression levels of 50 percent or better can be expected.

Upvotes: 3

Dan8080
Dan8080

Reputation: 66

First, run the LZW compression, this yields compressed data in binary format. Next then do base-64 encoding on the the compressed binary data. This will yield a text version of the compressed data that you can store in your database.

To restore the contents, do the base-64 decode. Then the LZW decompression.

There are Java libraries to do both. Just search on "LZW compression Java" and on "base-64 encode Java".

Upvotes: 0

Stephen
Stephen

Reputation: 18964

Well, you couldn't use gzip comppression. See here: Why can't browser send gzip request?

I suppose you could strip whitespace, but that would prove unsustainable. I'm not sure if this is an itch that needs scratching.

I did find this with a google search: http://rumkin.com/tools/compression/compress_huff.php That will eventually yield a smaller set of text, if the text is large enough. It actually inflates the text if the text is short.

I also found this: http://www.sean.co.uk/a/webdesign/javascript_string_compression.shtm

Upvotes: 0

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