Diffpatcher is a small library that lets you treat hashes as if they were git repositories.

Diff function that takes two hashes and returns delta hash.

var diff = require("diffpatcher/diff")

diff({ a: { b: 1 }, c: { d: 2 } },      // hash#1
     { a: { e: 3 }, c: { d: 4 } })      // hash#2

// => {                                 // delta
//      a: {
//        b: null,        // -
//        e: 3            // +
//      },
//      c: {
//        d: 4            // ±
//      }
//    }

As you can see from the example above delta makes no real distinction between proprety upadate and property addition. Try to think of additions as an update from undefined to whatever it's being updated to.

Patch fuction takes a hash and a delta and returns a new hash which is just like orginial but with delta applied to it. Let's apply delta from the previous example to the first hash from the same example

var patch = require("diffpatcher/patch")

patch({ a: { b: 1 }, c: { d: 2 } },     // hash#1
      {                                 // delta
        a: {
          b: null,        // -
          e: 3            // +
        },
        c: {
          d: 4            // ±
        }
      })

// => { a: { e: 3 }, c: { d: 4 } }      // hash#2

That's about it really, just diffing hashes and applying thes diffs on them.

And as Linus mentioned everything in git can be expressed with rebase, that also pretty much the case for diffpatcher. rebase takes target hash, and rebases parent onto it with diff applied.

npm install diffpatcher