sample extend

lang.extend.js

var lang = function(){};

lang.extend = lang.prototype.extend = function(){
    var len = arguments.length,
        target = {},
        options, name, src, copy, clone, i= 0;

    if (len === 1) {
        target = this;
    } else if(len > 1) {
        target = arguments[0];
        i = 1;
    }


    for (; i < len; i++) {
        options = arguments[i];
        for (name in options) {
            src = target[name];
            copy = options[name];

            if (target == copy) {
                continue;
            }

            if (typeof copy === 'object' || Array.isArray(copy)) {
                if (Array.isArray(copy)) {
                    clone = Array.isArray(src) ? src : [];
                } else {
                    clone = (typeof src === 'object') ? src : {};
                }
                target[name] = lang.extend.call(target, clone, copy);
            } else if (copy !== undefined) {
                target[name] = copy;
            }
        }
    }

    return target;
};