Deep (recursive) diff function implementation in Angular, lodash and ES6 / ES2015.

deep-diff-angular.js

function deepDiffRight (left, right) {
  // if they are equals, return undefined
  if (angular.equals(left, right)) return
  // form now on, we can assure that `left` and `right` are not equals (equivalents)
  
  // if `left` and `right` are primitives, value changed
  // if `left` is a primitive and `right` an object, value has been replaced with an object
  // if `left` is an object and `right` a primitive, value has been replaced with a primitive
  // use `_.copy` to prevent object referrence issues
  if (!angular.isObject(left) || !angular.isObject(right)) return angular.copy(right)
  
  // make `result` the same type as `right`
  var result = angular.isArray(right) ? [] : {}

  // since we know that both are objects,
  // iterate on `right` to see what changed or what's new in `right`
  angular.forEach(right, function (value, key) {
    // recursion
    var diff = deepDiffRight(left[key], right[key])
    // since the function returns undefined when `left` and `right` are equals,
    // only assing non-undefined values to result
    if (!angular.isUndefined(diff)) result[key] = diff
  });

  return result
}

deep-diff-lodash.js

_.mixin({ 'deepDiffRight': function deepDiffRight (left, right) {
  // if they are equals, return undefined
  if (_.isEqual(left, right)) return
  // form now on, we can assure that `left` and `right` are not equals (equivalents)

  // if `left` and `right` are primitives, value changed
  // if `left` is a primitive and `right` an object, value has been replaced with an object
  // if `left` is an object and `right` a primitive, value has been replaced with a primitive
  // use `_.cloneDeep` to prevent object referrence issues
  if (!_.isObject(left) || !_.isObject(right)) return _.cloneDeep(right)

  // since we know that both are objects,
  // iterate on `right` to see what changed or what's new in `right`
  return _.transform(right, function (result, n, key) {
    // recursion
    var diff = deepDiffRight(left[key], right[key])
    // since the function returns undefined when `left` and `right` are equals,
    // only assing non-undefined values to result
    if (diff !== undefined) result[key] = diff
  })
}})