javascript - 如何限制else语句？ - Javascript 游戏

Question

我正在寻找有关如何正确实现您站立的“按钮”(正方形)的解释，这将改变背景颜色。我已经成功实现了 if 语句，它改变了背景，但是当我添加一个 else 语句将它改回正常时，当你不在按钮上时，它会重复运行而不会停止。

我遇到的另一个障碍物也是如此，它会让你站在上面时移动速度变慢。当您不在障碍物上时，它会不断更改变量，而不是一次将其更改回来。

var gravity = 30;
var jumpSpeed = 17;
var playerYSpeed = 7;

Player.prototype.moveY = function(step, level, keys, pos) {
  this.speed.y += step * gravity;
  var motion = new Vector(0, this.speed.y * step);
  var newPos = this.pos.plus(motion);
  var obstacle = level.obstacleAt(newPos, this.size);
  var lastObstacle = null;

  if (obstacle) {
      if (keys.up && this.speed.y > 0)
        this.speed.y = -jumpSpeed;
      else
        this.speed.y = 0;
    } else {
      this.pos = newPos;
    }
  if (obstacle === "lava") {
    this.pos = new Vector(6.5, 18.5);
  }
  if (obstacle === "bouncer") {
    this.pos = newPos + 20;
    console.log('bounce');
  }
  else {
    gravity = 30;
  }
  if (obstacle === "ice") {
    playerXSpeed = 0.5;
    console.log('slow speed');
  }
  else if (obstacle !== lastObstacle){
    playerXSpeed = 7;
    console.log('norm speed');
  }
  var changeBackground = document.getElementsByClassName('background');
  if (obstacle === "blind") {
      changeBackground[0].style.background = 'white';
      console.log('purple');
    }
  else if (obstacle !== lastObstacle){
      changeBackground[0].style.background = 'blue';
      console.log('blue');
  }
};

“盲”障碍应该只有当你站在上面时才会改变背景，当你离开时它应该恢复正常。冰也一样。

那么您如何使它更像是“打开”-“关闭”场景？

Answer 1

如果我正确理解您的代码，它在某个循环函数中。

您可以添加一个变量“lastObstacle”并检查当前障碍物是否不同。 (else if (lastObstacle !== obstacle)

var gravity = 30;
var jumpSpeed = 17;
var playerYSpeed = 7;
var lastObstacle = null;

Player.prototype.moveY = function(step, level, keys, pos) {
  this.speed.y += step * gravity;
  var motion = new Vector(0, this.speed.y * step);
  var newPos = this.pos.plus(motion);
  var obstacle = level.obstacleAt(newPos, this.size);

  if (obstacle) {
      if (keys.up && this.speed.y > 0)
        this.speed.y = -jumpSpeed;
      else
        this.speed.y = 0;
    } else {
      this.pos = newPos;
    }
  if (obstacle === "lava") {
    this.pos = new Vector(6.5, 18.5);
  }
  if (obstacle === "bouncer") {
    this.pos = newPos + 20;
    console.log('bounce');
  }
  else {
    gravity = 30;
  }
  if (obstacle === "ice") {
    playerXSpeed = 0.5;
    console.log('slow speed');
  }
  else if (obstacle !== lastObstacle){
    playerXSpeed = 7;
    console.log('norm speed');
  }
  var changeBackground = document.getElementsByClassName('background');
  if (obstacle === "blind") {
      changeBackground[0].style.background = 'white';
      console.log('purple');
    }
  else if (obstacle !== lastObstacle){
      changeBackground[0].style.background = 'blue';
      console.log('blue');
  }
  lastObstacle = obstacle;
};

(评论:片段可能不起作用。)

PS:我犯了一个小错误，我现在更正了:

var gravity = 30;
var jumpSpeed = 17;
var playerYSpeed = 7;
var lastObstacle = null;

Player.prototype.moveY = function(step, level, keys, pos) {
  this.speed.y += step * gravity;
  var motion = new Vector(0, this.speed.y * step);
  var newPos = this.pos.plus(motion);
  var obstacle = level.obstacleAt(newPos, this.size);

  if (obstacle) {
      if (keys.up && this.speed.y > 0)
        this.speed.y = -jumpSpeed;
      else
        this.speed.y = 0;
    } else {
      this.pos = newPos;
    }
  if (obstacle === "lava") {
    this.pos = new Vector(6.5, 18.5);
  }
  if (obstacle === "bouncer") {
    this.pos = newPos + 20;
    console.log('bounce');
  }
  else {
    gravity = 30;
  }
  if (obstacle === "ice") {
    playerXSpeed = 0.5;
    console.log('slow speed');
  }
  else if (lastObstacle === "ice"){
    playerXSpeed = 7;
    console.log('norm speed');
  }
  var changeBackground = document.getElementsByClassName('background');
  if (obstacle === "blind") {
      changeBackground[0].style.background = 'white';
      console.log('purple');
    }
  else if (lastObstacle === "blind"){
      changeBackground[0].style.background = 'blue';
      console.log('blue');
  }
  lastObstacle = obstacle;
};

我更改了 lastObstacle !== obstacle 的两次出现。

编辑 2:它是这样工作的:只有当你现在不在冰 block /盲 block 上并且你之前在冰 block /盲 block 上时，它才会执行 else-if block 。