const FunProp = Function.prototype;

FunProp.before = function (beforeFn) {
  const _self = this;

  return function () {
    // 先执行before函数，再执行原函数
    beforeFn.apply(this, arguments);
    return _self.apply(this, arguments);
  }
}

FunProp.after = function (afterFn) {
  const _self = this;
  return function () {
    // 先执行原函数，再执行after函数
    const ret = _self.apply(this, arguments);
    afterFn.apply(this, arguments);
    return ret;
  }
}

function test() {
	console.log("test");
}

const _test = test
	.before(function(){console.log("before")})
	.after(function(){console.log("after")});
	
_test();