class Player { constructor(x, y, radius, color, vector) { this.x = x; this.y = y; this.radius = radius; this.color = color; this.vector = vector; this.life = 3;//玩家生命值 } draw(ctx) { ctx.save(); ctx.beginPath(); ctx.fillStyle = this.color; ctx.arc(this.x, this.y, this.radius, 0, Math.PI * 2, false); ctx.fill(); ctx.closePath(); ctx.restore(); } resize(x, y) { this.x = x; this.y = y; } } class Enemy { constructor(x, y, radius, color, vector) { this.x = x; this.y = y; this.radius = radius; this.color = color; this.vector = vector; } draw(ctx) { ctx.save(); ctx.beginPath(); ctx.fillStyle = this.color; ctx.arc(this.x, this.y, this.radius, 0, Math.PI * 2, false); ctx.fill(); ctx.closePath(); ctx.restore(); } update() { this.x += this.vector.x; this.y += this.vector.y; } } 要为玩家添加生命值。判断敌人与玩家是否撞击，是则玩家的生命值减1当玩家生命值减到0时，游戏结束。

可以在 `Player` 类中添加一个 `life` 属性来表示玩家的生命值，并将其初始化为 3。然后在 `Enemy` 类中添加一个 `checkCollision()` 方法来检测敌人与玩家是否撞击，如果撞击，则将玩家的生命值减 1。在 `Player` 类中添加一个 `checkGameOver()` 方法来检测玩家生命值是否减为 0，如果减为 0，则游戏结束。

下面是修改后的代码：

class Player {
  constructor(x, y, radius, color, vector) {
    this.x = x;
    this.y = y;
    this.radius = radius;
    this.color = color;
    this.vector = vector;
    this.life = 3; // 玩家生命值
  }
  
  draw(ctx) {
    ctx.save();
    ctx.beginPath();
    ctx.fillStyle = this.color;
    ctx.arc(this.x, this.y, this.radius, 0, Math.PI * 2, false);
    ctx.fill();
    ctx.closePath();
    ctx.restore();
  }
  
  resize(x, y) {
    this.x = x;
    this.y = y;
  }
  
  checkGameOver() {
    if (this.life === 0) {
      // 游戏结束
      console.log('Game over');
    }
  }
}

class Enemy {
  constructor(x, y, radius, color, vector) {
    this.x = x;
    this.y = y;
    this.radius = radius;
    this.color = color;
    this.vector = vector;
  }
  
  draw(ctx) {
    ctx.save();
    ctx.beginPath();
    ctx.fillStyle = this.color;
    ctx.arc(this.x, this.y, this.radius, 0, Math.PI * 2, false);
    ctx.fill();
    ctx.closePath();
    ctx.restore();
  }
  
  update() {
    this.x += this.vector.x;
    this.y += this.vector.y;
  }
  
  checkCollision(player) {
    const distance = Math.sqrt((player.x - this.x) ** 2 + (player.y - this.y) ** 2);
    if (distance < player.radius + this.radius) {
      // 玩家与敌人撞击，玩家生命值减1
      player.life--;
      console.log('Life:', player.life);
    }
  }
}