ES6形参默认值

* 形参的默认值----当不传入参数的时候默认使用形参里的默认值

   function Point(x = ,y = ) {
    this.x = x;
    this.y = y;
    }

 //定义一个点的坐标
    function Point(x=, y=) {
        this.x = x;
        this.y = y;
    }
    let point = new Point(, );
    console.log(point);
    let p = new Point();
    console.log(p);
    let point1 = new Point(, );
    console.log(point1);