deepExtend.js

var _hasOwn = Object.prototype.hasOwnProperty;
var _toString = Object.prototype.toString;
var _hasGOPD = typeof Object.getOwnPropertyDescriptor === 'function';
var _hasDP = typeof Object.defineProperty === 'function';

function _getOwnPropertyDescriptor(obj, prop) {
    if ( _hasGOPD ) {
        return Object.getOwnPropertyDescriptor(obj, prop)
    }
    else {
        return { 'value': obj[prop], 'writable': true, 'configurable': true, 'enumerable': true };
    }
}

function _defineProperty(obj, prop, descriptor) {
    if ( _hasDP ) {
        Object.defineProperty(obj, prop, descriptor);
    }
    else {
        obj[prop] = descriptor['value'];
    }
}

function _deepExtend(target) {    
    for(var i = 1; i < arguments.length; i++) {
        var donor = arguments[i];

        if(typeof donor == "object" && donor) {
            for ( var prop in donor ) if ( _hasOwn.call(donor, prop) ) {
                var propDesc = _getOwnPropertyDescriptor(donor, prop),
                    target_propDesc;

                if ( _toString.call(propDesc.value) == "[object Object]"/* && !(prop in target)*/ ) {
                    target[prop] = _deepExtend({}, donor[prop]);
                }
                else if ( _toString.call(propDesc.value) == "[object Array]"/* && !(prop in target)*/ ) {
                    target[prop] = _deepExtend([], donor[prop]);
                }
                else if ( !(target_propDesc = _getOwnPropertyDescriptor(target, prop))
                          || typeof target_propDesc.value !== "object" ) {
                    if( !target_propDesc
                        || ( "value" in target_propDesc
                            ? target_propDesc.value != propDesc.value
                            : target_propDesc.get !== propDesc.get || target_propDesc.set !== propDesc.set )
                        && target_propDesc.configurable !== false
                    ) {
                        _defineProperty(target, prop, propDesc);
                    }
                }
                else {
                    _deepExtend(target[prop], donor[prop]);
                }
            };
        }
    }
    return target;
}

module.exports = _deepExtend;