✏ EDIT: clone.js

var clone = (function() {
'use strict';

/**
 * Clones (copies) an Object using deep copying.
 *
 * This function supports circular references by default, but if you are certain
 * there are no circular references in your object, you can save some CPU time
 * by calling clone(obj, false).
 *
 * Caution: if `circular` is false and `parent` contains circular references,
 * your program may enter an infinite loop and crash.
 *
 * @param `parent` - the object to be cloned
 * @param `circular` - set to true if the object to be cloned may contain
 *    circular references. (optional - true by default)
 * @param `depth` - set to a number if the object is only to be cloned to
 *    a particular depth. (optional - defaults to Infinity)
 * @param `prototype` - sets the prototype to be used when cloning an object.
 *    (optional - defaults to parent prototype).
*/
function clone(parent, circular, depth, prototype) {
  var filter;
  if (typeof circular === 'object') {
    depth = circular.depth;
    prototype = circular.prototype;
    filter = circular.filter;
    circular = circular.circular
  }
  // maintain two arrays for circular references, where corresponding parents
  // and children have the same index
  var allParents = [];
  var allChildren = [];

var useBuffer = typeof Buffer != 'undefined';

if (typeof circular == 'undefined')
    circular = true;

if (typeof depth == 'undefined')
    depth = Infinity;

// recurse this function so we don't reset allParents and allChildren
  function _clone(parent, depth) {
    // cloning null always returns null
    if (parent === null)
      return null;

if (depth == 0)
      return parent;

var child;
    var proto;
    if (typeof parent != 'object') {
      return parent;
    }

if (clone.__isArray(parent)) {
      child = [];
    } else if (clone.__isRegExp(parent)) {
      child = new RegExp(parent.source, __getRegExpFlags(parent));
      if (parent.lastIndex) child.lastIndex = parent.lastIndex;
    } else if (clone.__isDate(parent)) {
      child = new Date(parent.getTime());
    } else if (useBuffer && Buffer.isBuffer(parent)) {
      if (Buffer.allocUnsafe) {
        // Node.js >= 4.5.0
        child = Buffer.allocUnsafe(parent.length);
      } else {
        // Older Node.js versions
        child = new Buffer(parent.length);
      }
      parent.copy(child);
      return child;
    } else {
      if (typeof prototype == 'undefined') {
        proto = Object.getPrototypeOf(parent);
        child = Object.create(proto);
      }
      else {
        child = Object.create(prototype);
        proto = prototype;
      }
    }

if (circular) {
      var index = allParents.indexOf(parent);

if (index != -1) {
        return allChildren[index];
      }
      allParents.push(parent);
      allChildren.push(child);
    }

for (var i in parent) {
      var attrs;
      if (proto) {
        attrs = Object.getOwnPropertyDescriptor(proto, i);
      }

if (attrs && attrs.set == null) {
        continue;
      }
      child[i] = _clone(parent[i], depth - 1);
    }

return child;
  }

return _clone(parent, depth);
}

/**
 * Simple flat clone using prototype, accepts only objects, usefull for property
 * override on FLAT configuration object (no nested props).
 *
 * USE WITH CAUTION! This may not behave as you wish if you do not know how this
 * works.
 */
clone.clonePrototype = function clonePrototype(parent) {
  if (parent === null)
    return null;

var c = function () {};
  c.prototype = parent;
  return new c();
};

// private utility functions

function __objToStr(o) {
  return Object.prototype.toString.call(o);
};
clone.__objToStr = __objToStr;

function __isDate(o) {
  return typeof o === 'object' && __objToStr(o) === '[object Date]';
};
clone.__isDate = __isDate;

function __isArray(o) {
  return typeof o === 'object' && __objToStr(o) === '[object Array]';
};
clone.__isArray = __isArray;

function __isRegExp(o) {
  return typeof o === 'object' && __objToStr(o) === '[object RegExp]';
};
clone.__isRegExp = __isRegExp;

function __getRegExpFlags(re) {
  var flags = '';
  if (re.global) flags += 'g';
  if (re.ignoreCase) flags += 'i';
  if (re.multiline) flags += 'm';
  return flags;
};
clone.__getRegExpFlags = __getRegExpFlags;

return clone;
})();

if (typeof module === 'object' && module.exports) {
  module.exports = clone;
}

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