clone.js

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

function _instanceof(obj, type) {
  return type != null && obj instanceof type;
}

var nativeMap;
try {
  nativeMap = Map;
} catch(_) {
  // maybe a reference error because no `Map`. Give it a dummy value that no
  // value will ever be an instanceof.
  nativeMap = function() {};
}

var nativeSet;
try {
  nativeSet = Set;
} catch(_) {
  nativeSet = function() {};
}

var nativePromise;
try {
  nativePromise = Promise;
} catch(_) {
  nativePromise = function() {};
}

/**
 * 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).
 * @param `includeNonEnumerable` - set to true if the non-enumerable properties
 *    should be cloned as well. Non-enumerable properties on the prototype
 *    chain will be ignored. (optional - false by default)
*/
function clone(parent, circular, depth, prototype, includeNonEnumerable) {
  if (typeof circular === 'object') {
    depth = circular.depth;
    prototype = circular.prototype;
    includeNonEnumerable = circular.includeNonEnumerable;
    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 (_instanceof(parent, nativeMap)) {
      child = new nativeMap();
    } else if (_instanceof(parent, nativeSet)) {
      child = new nativeSet();
    } else if (_instanceof(parent, nativePromise)) {
      child = new nativePromise(function (resolve, reject) {
        parent.then(function(value) {
          resolve(_clone(value, depth - 1));
        }, function(err) {
          reject(_clone(err, depth - 1));
        });
      });
    } else 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.from) {
        // Node.js >= 5.10.0
        child = Buffer.from(parent);
      } else {
        // Older Node.js versions
        child = new Buffer(parent.length);
        parent.copy(child);
      }
      return child;
    } else if (_instanceof(parent, Error)) {
      child = Object.create(parent);
    } 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);
    }

    if (_instanceof(parent, nativeMap)) {
      parent.forEach(function(value, key) {
        var keyChild = _clone(key, depth - 1);
        var valueChild = _clone(value, depth - 1);
        child.set(keyChild, valueChild);
      });
    }
    if (_instanceof(parent, nativeSet)) {
      parent.forEach(function(value) {
        var entryChild = _clone(value, depth - 1);
        child.add(entryChild);
      });
    }

    for (var i in parent) {
      var attrs = Object.getOwnPropertyDescriptor(parent, i);
      if (attrs) {
        child[i] = _clone(parent[i], depth - 1);
      }

      try {
        var objProperty = Object.getOwnPropertyDescriptor(parent, i);
        if (objProperty.set === 'undefined') {
          // no setter defined. Skip cloning this property
          continue;
        }
        child[i] = _clone(parent[i], depth - 1);
      } catch(e){
        if (e instanceof TypeError) {
          // when in strict mode, TypeError will be thrown if child[i] property only has a getter
          // we can't do anything about this, other than inform the user that this property cannot be set.
          continue
        } else if (e instanceof ReferenceError) {
          //this may happen in non strict mode
          continue
        }
      }

    }

    if (Object.getOwnPropertySymbols) {
      var symbols = Object.getOwnPropertySymbols(parent);
      for (var i = 0; i < symbols.length; i++) {
        // Don't need to worry about cloning a symbol because it is a primitive,
        // like a number or string.
        var symbol = symbols[i];
        var descriptor = Object.getOwnPropertyDescriptor(parent, symbol);
        if (descriptor && !descriptor.enumerable && !includeNonEnumerable) {
          continue;
        }
        child[symbol] = _clone(parent[symbol], depth - 1);
        Object.defineProperty(child, symbol, descriptor);
      }
    }

    if (includeNonEnumerable) {
      var allPropertyNames = Object.getOwnPropertyNames(parent);
      for (var i = 0; i < allPropertyNames.length; i++) {
        var propertyName = allPropertyNames[i];
        var descriptor = Object.getOwnPropertyDescriptor(parent, propertyName);
        if (descriptor && descriptor.enumerable) {
          continue;
        }
        child[propertyName] = _clone(parent[propertyName], depth - 1);
        Object.defineProperty(child, propertyName, descriptor);
      }
    }

    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;
}