canon

CANON

CANON is canonical object notation. It closely resembles JSON. In fact, CANON.stringify and CANON.parse make use of their JSON counterparts internally.

What's wrong with JSON?

JSON is great for passing around serialized data. There's a second reason one might wish to serialize data, though: to implement efficient sets and dictionaries, two useful data structures JavaScript currently lacks.

In order to implements sets and dictionaries efficiently, one needs to be able to hash values consistently. JSON.stringify does not guarantee the order of object keys, so cannot be relied upon.

Implementing sets with CANON

The only data structure JavaScript currently provides for dealing with unique collections is the humble object. Only strings can be used as keys, though, so it's necessary to serialize each value that's added to the set. This yields a data structure mapping serialized values to the values themselves:

CANON.stringify(value1) ➞ value1
CANON.stringify(value2) ➞ value2
...
CANON.stringify(valueN) ➞ valueN

To limit the length of the keys (and thus the memory footprint), a hashing function can be used:

sha256(CANON.stringify(value1)) ➞ value1
sha256(CANON.stringify(value2)) ➞ value2
...
sha256(CANON.stringify(valueN)) ➞ valueN

A simple set implementation might resemble the following:

hash = (value) -> sha256 CANON.stringify value

class Set
  constructor: (values...) ->
    @values = {}
    @add values...
  contains: (value) ->
    Object::hasOwnProperty.call @values, hash value
  add: (values...) ->
    for value in values
      @values[hash value] = value
    return
  remove: (values...) ->
    for value in values
      delete @values[hash value]
    return
  each: (iterator) ->
    for own key, value of @values
      iterator value
    return

coffee> points = new Set [1,2], [5,2], [3,6]
{ values:
   { '736e4ff990cbad3e9ed1b2d78abfea3bd73a5e773960f40fbbc42e490df999bf': [ 1, 2 ],
     '41cc5c39058d6626dfa57703740a21676229901e1a26f844fc96cb7462e05828': [ 5, 2 ],
     'cd326a88a511fc5ca7831944f0f2a3091273faf7e5fbec3f8e482ace48392657': [ 3, 6 ] } }
coffee> points.contains [4,4]
false
coffee> points.contains [5,2]
true
coffee> points.each (point) -> console.log point
[ 1, 2 ]
[ 5, 2 ]
[ 3, 6 ]
undefined

Differences between CANON and JSON

> CANON.stringify(-0)                       > JSON.stringify(-0)
'-0'                                        '0'
> CANON.stringify([1, 2, 3])                > JSON.stringify([1, 2, 3])
'["Array",1,2,3]'                           '[1,2,3]'
> CANON.stringify(new Date(1350246457000))  > JSON.stringify(new Date(1350246457000))
'["Date","2012-10-14T20:27:37.000Z"]'       '"2012-10-14T20:27:37.000Z"'
> CANON.stringify(Infinity)                 > JSON.stringify(Infinity)
'["Number","Infinity"]'                     'null'
> CANON.stringify(-Infinity)                > JSON.stringify(-Infinity)
'["Number","-Infinity"]'                    'null'
> CANON.stringify(NaN)                      > JSON.stringify(NaN)
'["Number","NaN"]'                          'null'
> CANON.stringify({foo:1, bar:2})           > JSON.stringify({foo:1, bar:2})
'["Object","bar",2,"foo",1]'                '{"foo":1,"bar":2}'
> CANON.stringify(/foo/i)                   > JSON.stringify(/foo/i)
'["RegExp","/foo/i"]'                       '{}'
> CANON.stringify(undefined)                > JSON.stringify(undefined)
'["Undefined"]'                             undefined
> CANON.stringify(function(){})             > JSON.stringify(function(){})
TypeError: Functions cannot be serialized   undefined

From the output of JSON.stringify it's not always possible to determine the input value:

> JSON.stringify(new Date(1350246457000)) === JSON.stringify('2012-10-14T20:27:37.000Z')
true

Since CANON.stringify includes type information for most values, different values with the same string representation (such as /foo/i and '/foo/i') are serialized differently. As a result, CANON.parse can materialize Date and RegExp objects:

> CANON.parse(CANON.stringify(new Date(1350246457000))) instanceof Date
true
> JSON.parse(JSON.stringify(new Date(1350246457000))) instanceof Date
false

Installation

Browser:

<script src="https://raw.github.com/davidchambers/CANON/master/lib/canon.js"></script>

Server:

$ npm install canon

Running the test suite

$ make setup
$ make test

To run the test suite in a browser, open test/index.html.

Related projects

• mirkokiefer/canonical-json