immutable-js/src/util/clone.js

Immutable types in JavaScript

/**
 *  Copyright (c) 2015, Jan Biasi.
 *  All rights reserved.
 *
 *  This source code is licensed under the BSD-style license found in the
 *  LICENSE file in the root directory of this source tree. An additional grant
 *  of patent rights can be found in the PATENTS file in the same directory.
 */

export default function clone(item) {
    if (!item) {
        // null, undefined values check
        return item;
    }

    var types = [Number, String, Boolean],
        result;

    // normalizing primitives if someone did new String('aaa'), or new Number('444');
    types.forEach(function(type) {
        if (item instanceof type) {
            result = type(item);
        }
    });

    if (typeof result === 'undefined') {
        if (Object.prototype.toString.call(item) === '[object Array]') {
            result = [];
            item.forEach(function(child, index, array) {
                result[index] = clone(child);
            });
        } else if (typeof item === 'object') {
            // testing that this is DOM
            if (item.nodeType && typeof item.cloneNode === 'function') {
                result = item.cloneNode(true);
            } else if (!item.prototype) { // check that this is a literal
                if (item instanceof Date) {
                    result = new Date(item);
                } else {
                    // it is an object literal
                    result = {};
                    for (var i in item) {
                        if(item.hasOwnProperty(i)) {
                            result[i] = clone(item[i]);
                        }
                    }
                }
            } else {
                // depending what you would like here,
                // just keep the reference, or create new object
                if (false && item.constructor) {
                    result = Object.create(item.prototype);
                } else {
                    result = item;
                }
            }
        } else {
            result = item;
        }
    }
    return result;
}