Js中所有函数都是Fuction的实例吗？
用 Proxy 很容易弄出一个「可以调用但不 isntanceof Function」的东西出来。

            function sum (a, b) {      return a + b;    }        const handler = {      getPrototypeOf(target) {        return null;      },      apply: function(target, thisArg, argumentsList) {        console.log(`Calculate sum: ${argumentsList}`);        // expected output: "Calculate sum: 1,2"            return target(argumentsList, argumentsList) * 10;      }    };        const proxy1 = new Proxy(sum, handler);        console.log(sum(1, 2));                  // => 3    console.log(proxy1(1, 2));               // => 30    console.log(proxy1 instanceof Function); // => false