@transformation-dev/deep-object-diff-apply

Take the output of deep-object-diff's diff() function, apply it to the original lhs, and you get the original rhs.

Installation

npm install @transformation-dev/deep-object-diff-apply

Usage

import { diff } from 'deep-object-diff';
import { applyDiff } from '@transformation-dev/deep-object-diff-apply';

const lhs = { a: 1, b: 2, c: 3 };
const rhs = { a: 1, b: 4, d: 5 };
const differences = diff(lhs, rhs);
const restoredRHS = applyDiff(lhs, differences);
expect(restoredRHS).toEqual(rhs);

Notes

This function modifies lhs in place to be optimal for updating a large object with a small diff you send over a network.

It assumes that the diff is in the format of deep-object-diff's diff() function. It does not work with the other deep-object-diff output formats (detailed, added, etc.). The diff() output format is the most compact which is what you want when sending over a network.

The tests come from deep-object-diff's test suite.

However, to get all of the tests to pass, I had to add quite a bit of complexity. When you compare two primatives (string, number, etc) or quasi-primative (String, Number, Date, etc.) deep-object-diff returns the rhs (quasi)primative as the diff. Maybe there is a more efficient way to test for this than what I've implemented, but this works at least for all of deep-object-diff's tests.

If you make the assumption that the lhs and rhs are both plain objects, then this code would be a lot simpler and would run faster. That said, I'm confident that even with this complexity, the time to apply the diff is a very small fraction of the transmission time of the diff itself and worth it to work correctly with every possible deep-object-diff output.