装饰者模式，after | before

Function.prototype.after&before.js

Function.prototype.after = function (fn) {
    var that = this;

    return function () {
        var ret = that.apply(this, arguments);

        fn.apply(this, arguments);

        return ret;
    };
};

Function.prototype.before = function (fn) {
    var that = this;

    return function () {
        fn.apply(this, arguments);

        return that.apply(this, arguments);
    };
};

var showLogin = function () {
    console.log('打开登陆框');
};

showLogin = showLogin.after(function () {
    console.log('上报登录统计');
});

showLogin();