canvas 中未将变量设置为矩形

Question

我试图通过将 1 添加到矩形的 x/y 位置来在您单击按钮时移动矩形，但速度变量一直显示未定义。

      // . . . //

      function component(width, height, color, x, y) {
      this.width = width;
      this.height = height;
      this.speedX = 0;
      this.speedY = 0;
      this.x = x;
      this.y = y;
      this.update = function(){
        ctx = gameArea.context;
        ctx.fillStyle = color;
        ctx.fillRect(this.x, this.y, this.width, this.height); 
      }
      this.newPos = function(){
        this.x += this.speedX;
        this.y += this.speedY;
      }
  }


    function updateGameArea(){// Update games at 50fps
       gameArea.clear();
       bluePiece.newPos();
       bluePiece.update();
  }


  function moveUp(piece){
    piece.speedY -= 1;
    console.log("UP "+piece+" S:"+piece.speedY);
  }
  function moveDown(piece){
    piece.speedY += 1;
    console.log("DOWN "+piece+" S:"+piece.speedY);
  }
  function moveLeft(piece){
    piece.speedX -= 1;
    console.log("LEFT "+piece+" S:"+piece.speedX);
  }
  function moveRight(piece){
    piece.speedY += 1;
    console.log("RIGHT "+piece+" S:"+piece.speedX);
  }

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Answer 1

你将一个字符串传递给函数，然后访问 String 的属性，这肯定是未定义的。
尝试 console.log(typeof piece);

canvas 中未将变量设置为矩形

Not setting variable to rectangle in canvas

javascript

variables

canvas

rectangles