我的变量之一被无故更改

Question

我正在p5.js中跟踪编码火车的飞扬的小鸟挑战。一切顺利，直到我尝试运行该程序为止，“ Pipes总是在我第一次跳动时向上移动。这是我第一次敲空格键。我对这里发生的事情一无所知。管道的位置值永远不会与keyPressed函数相交，因此我很好奇管道向上移动的位置。

let bird;
let pipes = [];
let pipe;

function setup() {
  createCanvas(400, 600);
  bird = new Bird();
  pipe = new Pipe();
  pipes.push(new Pipe());
}

function draw() {
  background(0);
  bird.update();
  bird.show();

  pipe.prints();
  for (let i = 0; i < pipes.length; i++) {
    pipe.prints();
    pipes[i].show();
    pipes[i].update();
    pipe.prints();
  }
  pipe.prints();
}

function keyPressed() {
  if (key == ' ') {
    bird.up();

}
function Bird() {
  this.x = 64;
  this.y = height / 2;

  this.gravity = 0.9;
  this.lift = -20;
  this.velocity = 0;

  this.show = function() {
    fill(255);
    ellipse(this.x, this.y, 32, 32);
  }

  this.up = function() {
    this.velocity += this.lift;
  }

  this.update = function() {
    this.velocity += this.gravity;
    this.velocity *= 0.9;
    this.y += this.velocity;

    if (this.y > height) {
      this.y = height;
      this.velocity = 0;
    }

    if (this.y < 0) {
      this.y = 0;
      this.velocity = 0;
    }

  }

}
function Pipe() {

  this.top = random(height / 2);
  this.bottom = random(height / 2);
  this.x = width;
  this.w = 20;
  this.speed = 3;

  this.show = function() {
    fill(255);
    rect(this.x, 0, this.w, this.top);
    rect(this.x, height - this.bottom, this.w, this.bottom);
  }

  this.update = function() {
    this.x -= this.speed;
  }
  this.prints = function() {
    print("Top: " + this.x + " Bottom: " + this.w);
  }
}