json-delta is an efficient, JSON oriented javascript object delta calculator and applier. It provides a configurable threshold (tolerance) after which the diff calculator will short circuit a more complex delta analysis, useful for calculating deltas on very large objects that may from time to time be fully replaced.

Unlike similar libraries, json-delta sacrifices certain features and makes certain sane assumptions that allow it to perform.

For instance, it treats undefined as null and does not preserve constructor or prototype-bound behaviors. Arrays are not diffed recursively -- any elements with property changes result in single replacement delta of that element. Objects are diffed recursively, however, so only the deepest nodes of a structure have their changes tracked.

diff(a, b, tolerance?) returns a simple array describing the changes needed to transform a to b. It will return null if a and b are deeply equal, and will return a single replacement delta if more than tolerance (number) of changes are found.

applyDiff(a, diff) returns an object that would be deeply equal to b.

applyDiff will not mutate the original a, although it may share references to container objects not changed in the patching. It uses shallow copying on any container that changes.

var jd = require("json-delta");
var diff = jd.diff([1, 2, 3], [1, 2, 3, 4]);
console.log(jd.applyDiff([1, 2, 3], diff));

npm install json-delta --save