Patcher.js

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A JSON patching and diffing library

(c) 2011 Mikola Lysenko

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1. About

patcher.js is a simple javascript library for diffing and patching JSON documents. This can be useful, for example, in a networked environment where retransmitting large JSON documents is too expensive.

2. Example:

//Start with two distinct objects on the server // prev represents a copy of the state of the object on the client // next represents a copy of the state of the object on the server // //1. Compute a patch patch = patcher.computePatch(prev, next);

//2. Send patch over the network

//3. Apply the patch on the client patcher.applyPatch(prev, patch);

//Final invariant: // prev represents an equivalent object to JSON.parse(JSON.stringify(next))

3. API

There are two functions in patcher.js:

function computePatch(prev, next, update_in_place);

The argument prev is the object which the patch targets.

* If update_in_place is set to true, then the function
will simultaneously update both prev and next at the same
time.
* If prev and next are equal, then the method returns null
* Constructing this patch requires time linear on the 
size of the two documents.
* Patches are computed at the level of the objects and
arrays.  String modifications are simply retransmitted

function applyPatch(obj, patch)

This function applies a patch to the JSON document obj

4. Future

• More test cases!
• Use data types cleverly
• Binary serialization