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 = 1,y = 2) {
this.x = x;
this.y = y;
}




//定义一个点的坐标
function Point(x=12, y=12) {
this.x = x;
this.y = y;
}
let point = new Point(25, 36);
console.log(point);
let p = new Point();
console.log(p);
let point1 = new Point(12, 35);
console.log(point1);