The Tor Browser / file revision

 "use strict";

 var method = require("../method/core")

 // Method is designed to work with data structures representing application

 // state. Calling it with a state should return object representing `delta`

 // that has being applied to a previous state to get to a current state.

 //

 // Example

 //

 // diff(state) // => { "item-id-1": { title: "some title" } "item-id-2": null }

 var diff = method("diff@diffpatcher")

 // diff between `null` / `undefined` to any hash is a hash itself.

 diff.define(null, function(from, to) { return to })

 diff.define(undefined, function(from, to) { return to })

 diff.define(Object, function(from, to) {

   return calculate(from, to || {}) || {}

 })

 function calculate(from, to) {

   var diff = {}

   var changes = 0

   Object.keys(from).forEach(function(key) {

     changes = changes + 1

     if (!(key in to) && from[key] != null) diff[key] = null

     else changes = changes - 1

   })

   Object.keys(to).forEach(function(key) {

     changes = changes + 1

     var previous = from[key]

     var current = to[key]

     if (previous === current) return (changes = changes - 1)

     if (typeof(current) !== "object") return diff[key] = current

     if (typeof(previous) !== "object") return diff[key] = current

     var delta = calculate(previous, current)

     if (delta) diff[key] = delta

     else changes = changes - 1

   })

   return changes ? diff : null

 }

 diff.calculate = calculate

 module.exports = diff