json-delta

Forked from corps/json-delta

Why a fork?

This for provides typings in the npm package. This fork will also be used to try and become more active for projects.

About json-delta

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));

Installation

npm i @clipchamp/json-delta

Using json-delta

json-delta supplies two pretty main/important functions, at least for clipchamp.

diff<T>

diff<T> takes two objects, and will return to you a Diff<T>. This diff object can only be applied to the type of object (supplied by T). For example:

const coordinates1: Coordinates = {
    x: 1,
    y: 0
};
const coordinates2: Coordinates = {
    x: 1,
    y: 1
};
// This will result in the type of Diff<Coordinates>
const diffBetweenCoordinates = diff(coordinates1, coordinates2);

The resulting diff will be something like:

const someDiff = {
    y: 0 => 1
}

applyDiff<T>

applyDiff<T> will allow you to apply a diff you previous collected, back onto the object (that follows the same generic typing of T).

const coordinates1As2 = applyDiff(coordiantes1, diffBetweenCoordinates);