扩展Javascript方法

今天新学一招,扩展一个方法,注释写的很清楚了,直接上代码

       <script>
        //首先注册全局变量ShowBook
        if (!window.ShowBook)
            var ShowBook = window.ShowBook = {
                F1: function() {
                    alert(1);
                },
                F2: function() {
                    alert(2);
                },
                Extend: function(dest, source, replace) {//扩展方法
                    for (prop in source) {
                        if (replace == false && dest[prop] != null) continue;
                        dest[prop] = source[prop];
                    };
                    return dest;
                }
            };
           
            (function() {       
                var extendFunction1 = {//待扩展的第一组方法
                    F3: function() {
                        alert(3);
                    },
                    F4: function() {
                        alert(4);
                    }
                };               
                var extendFunction2 = {//待扩展的第二组方法
                    F5: function() {
                        alert(5);
                    },
                    F6: function() {
                        alert(6);
                    }
                };
                //扩展第一组方法
                ShowBook.Extend(ShowBook, extendFunction1, false);
                //扩展第二组方法
                ShowBook.Extend(ShowBook, extendFunction2, false);
            })();

            //调用
            ShowBook.F1();
            ShowBook.F3();
            ShowBook.F5();
    </script>