怎么理解这道题的

function test() {
            this.flag = false;
            this.change = () => {
                // console.log(this) //test
                this.flag = true;
                console.log("button.flag",button.flag); //true
            };
        }
        const button = new test();
        document.addEventListener("click", button.change);

        function btn(){
            const button2 = new test()
            console.log("button2.flag",button2.flag) //false
        }