您好,我在尝试运行此代码时收到上述错误消息,但我无法弄清楚它出了什么问题,非常感谢您的帮助。请原谅您可能遇到的任何新手错误。我已经创建了一个球,并且正在尝试移动它。
class Ball{
constructor(x,y,xSpeed,ySpeed,r){
this.x =x;
this.y=y;
this.xSpeed=xSpeed;
this.ySpeed=ySpeed;
this.r= r;
}
draw(){
ctx.clearRect(0,0, 500, 200);
ctx.beginPath();
ctx.arc(this.x, this.y, this.r, 0, 2 * Math.PI);
ctx.stroke();
}
move()
{
this.x+=this.xSpeed; //error is here
this.y+=this.ySpeed;
if (this.x==0)
{
this.xSpeed=2;
}
else if(this.x==500)
{
this.xSpeed=-2;
}
if (this.y==200)
{
this.ySpeed=-1;
}
else if (this.y==0)
{
this.ySpeed=1;
}
window.requestAnimationFrame(this.move);
}
}
var canvas = document.getElementById("canvas-for-ball");
var ctx = canvas.getContext("2d")
let balls=new Ball (10,10,2,1,5);
balls.draw();
balls.move();
最佳答案
问题是当你调用requestAnimationFrame
时并将其传递给 move
的引用作为其回调, this
绑定(bind)到您的Ball
执行回调时实例会丢失。相反,您必须传递 move
以这样的方式 this
仍然绑定(bind)到您的Ball
实例。您可以通过使用 .bind()
传递函数引用来完成此操作。方法,它采用一个参数来指定 this
的内容绑定(bind)将在回调函数运行时进行。
class Ball {
constructor(x,y,xSpeed,ySpeed,r){
this.x = x;
this.y = y;
this.xSpeed = xSpeed;
this.ySpeed = ySpeed;
this.r = r;
}
draw(){
ctx.clearRect(0,0, 500, 200);
ctx.beginPath();
ctx.arc(this.x, this.y, this.r, 0, 2 * Math.PI);
ctx.stroke();
}
move(){
this.x += this.xSpeed;
this.y += this.ySpeed;
if (this.x == 0) {
this.xSpeed = 2;
} else if(this.x == 500) {
this.xSpeed =- 2;
}
if (this.y == 200) {
this.ySpeed =- 1;
} else if (this.y == 0) {
this.ySpeed = 1;
}
window.requestAnimationFrame(this.move.bind(this));
}
}
var canvas = document.getElementById("canvas-for-ball");
var ctx = canvas.getContext("2d")
let balls = new Ball(10,10,2,1,5);
balls.draw();
balls.move();
<canvas id="canvas-for-ball"></canvas>
关于javascript - Node.js -未捕获类型错误 : Cannot read property 'x' of undefined at object (ball,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/58160079/