gecko-dev/toolkit/modules/CanonicalJSON.jsm

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this file,
 * You can obtain one at http://mozilla.org/MPL/2.0/. */

var EXPORTED_SYMBOLS = ["CanonicalJSON"];

var CanonicalJSON = {
  /**
   * Return the canonical JSON form of the passed source, sorting all the object
   * keys recursively. Note that this method will cause an infinite loop if
   * cycles exist in the source (bug 1265357).
   *
   * @param source
   *        The elements to be serialized.
   *
   * The output will have all unicode chars escaped with the unicode codepoint
   * as lowercase hexadecimal.
   *
   * @usage
   *        CanonicalJSON.stringify(listOfRecords);
   **/
  stringify: function stringify(source, jsescFn) {
    if (typeof jsescFn != "function") {
      const { jsesc } = ChromeUtils.import(
        "resource://gre/modules/third_party/jsesc/jsesc.js"
      );
      jsescFn = jsesc;
    }
    if (Array.isArray(source)) {
      const jsonArray = source.map(x => (typeof x === "undefined" ? null : x));
      return (
        "[" + jsonArray.map(item => stringify(item, jsescFn)).join(",") + "]"
      );
    }

    if (typeof source === "number") {
      if (source === 0) {
        return Object.is(source, -0) ? "-0" : "0";
      }
    }

    // Leverage jsesc library, mainly for unicode escaping.
    const toJSON = input => jsescFn(input, { lowercaseHex: true, json: true });

    if (typeof source !== "object" || source === null) {
      return toJSON(source);
    }

    // Dealing with objects, ordering keys.
    const sortedKeys = Object.keys(source).sort();
    const lastIndex = sortedKeys.length - 1;
    return (
      sortedKeys.reduce((serial, key, index) => {
        const value = source[key];
        // JSON.stringify drops keys with an undefined value.
        if (typeof value === "undefined") {
          return serial;
        }
        const jsonValue = value && value.toJSON ? value.toJSON() : value;
        const suffix = index !== lastIndex ? "," : "";
        const escapedKey = toJSON(key);
        return (
          serial + escapedKey + ":" + stringify(jsonValue, jsescFn) + suffix
        );
      }, "{") + "}"
    );
  },
};