JsonOptimize (json-optimize)

Optimize objects prior to JSON encoding by analyzing property names, and temporarily replacing them with shorter ones based on combined length and number of occurences. Corresponding function to restore the original object.

Obviously this does not always produce smaller documents, but for some cases where property names are repeated a lot of times in e.g. an array of similar documents it can help.

It's not optimized for speed or anything.

License

MIT.

But there's MsgPack?!

Sure, but this works well in combination with MsgPack also:

Example test file:

• Original: 3 106 646
• MsgPack'ed: 2 417 832
• JsonOptimize'd: 2 161 369
• JsonOptimize'd then MsgPack'ed: 1 472 453

(See other test example at the bottom of this page)

Usage

Node.js

var fs = require('fs');
var JsonOptimize = require('json-optimize');

// read some json
var doc = JSON.parse(fs.readFileSync('junk.json'));

// create optimized document
var jo = new JsonOptimize();
var optDoc = jo.pack(doc);

// translate back to original
var origDoc = jo.unpack(optDoc);

JavaScript

<script type="text/javascript" src="bower_components/json-optimize/build/json-optimize.min.js"></script>
<script type="text/javascript">
var jo = new JsonOptimize();
var bar = ..;
var opt = jo.pack(bar);
var orig = jo.unpack(opt);
</script>

API

Constructor

new JsonOptimize([options])

options is an optional object with various overrides:

• idChars: which characters to use in ID generation (defaults: equivalent of [\x20-2F\x3A-7E\x20] [a-zA-Z]). (See note on object property order below)
• omitUndefined: skip undefined values in the analysis process, as they will be removed by the JSON serialization anyhow (default: true)
• excludeTypes: either an array of object types to not recurse into, or a function that will be called for each value (true: exclude, false: include). (default: [Date]).

Methods

pack(originalObject) : optimizedObject

unpack(optimizedObject) : originalObject

Implementation

The "optimized" document is basically in the form of an array with the first element being an array of the original key names, and the second element is the original document with propert names replaced.

Tests

• npm test - regular sanity checks
• npm run-script test-size - test performance

Notes

Circular references

There is no protection against circular references built-in. It will most likely go into an eternal loop, eventually blowing the call stack or running out of memory, whichever comes first. You should not be passing such objects into JSON.stringify() anyhow.

Object property order

According to the EcmaScript specification, the order of properties in an object is not really defined, but in most implementations (including Node.js and most browsers), the order is kept as long as the property name does not consist of only numerals, which appear in sorted order at the "beginning" of the object.

See: http://stackoverflow.com/a/5525812

I.e.: If you include '0'..'9' in the idChars option, do not expect property order to be preserved. But you shouldn't expect that anyhow.

Other example tests

Testing against a sample JSON file of all sets of MTG cards:

The question obviously is: with json + deflate/gzip being this close in byte savings, and also considerably faster, is there really anything to win from this? I don't know. I had fun writing this anyhow :P