json8-merge-patch/lib/diff.js

JSON Merge Patch toolkit for JavaScript

"use strict";

const type = require("json8/lib/type");
const equal = require("json8/lib/equal");
const OBJECT = "object";

module.exports = function diff(a, b) {
  const t = type(a);
  if (t !== OBJECT || t !== type(b)) return b;

  const patch = {};

  let keys, i, l, k;

  keys = Object.keys(b);
  for (i = 0, l = keys.length; i < l; i++) {
    k = keys[i];
    // added properties
    if (!a.hasOwnProperty(k)) patch[k] = b[k];
    // replaced properties
    else if (!equal(a[k], b[k])) patch[k] = diff(a[k], b[k]);
  }

  // removed properties
  keys = Object.keys(a);
  for (i = 0, l = keys.length; i < l; i++) {
    k = keys[i];
    if (!b.hasOwnProperty(k)) patch[k] = null;
  }

  return patch;
};