我试着用画布显示形状，但它们没有出现

Question

我正在做一个简单的游戏(学习Zenva学院的教程)，虽然我遵循了T的说明，但我似乎无法在浏览器中显示我的画布形状。下面是我到目前为止掌握的代码：

​

var canvas = document.getElementByID('myCanvas');
var ctx = canvas.getContext('2d');

let screenWidth = 1000;
let screenHeight = 500;

class GameCharacter {
  constructor(x, y, width, height, color) {
    this.x = x;
    this.y = y;
    this.width = width;
    this.height = height;
    this.color = color;
  }
}

var blueSquare = new GameCharacter(
  50, 50, 50, 50, "rgb(0, 0, 255)"
);
var rectangle = new GameCharacter(
  75, 75, 100, 50, "rgb(0, 255, 0)"
);
var redSquare = new GameCharacter(
  100, 50, 50, 50, "rgb(255, 0, 0)"
);

var draw = function() {
  ctx.clearRect(0, 0, screenWidth, screenHeight);

  ctx.fillStyle = "rgb(0, 0, 255)";
  ctx.fillRect(blueSquare.x, blueSquare.y, blueSquare.width, blueSquare.height);

  ctx.fillStyle = rectangle.color;
  ctx.fillRect(rectangle.x, rectangle.y, rectangle.width, rectangle.height);

  ctx.fillStyle = redSquare.color;
  ctx.fillRect(redSquare.x, redSquare.y, redSquare.width, redSquare.height);

}

var step = function() {
  draw();

  window.requestAnimationFrame(step);
}

canvas {
  border: 4px solid green;
  background-color: yellow;
}

<canvas id='myCanvas' width='1000' height='500'></canvas>

​

我对此还很陌生，这是我在论坛上提出的第一个问题。如果我做错了什么请告诉我。LOL!

我正在使用的：

操作系统： Windows 10 Pro 64位

浏览器：尝试了Chrome和Microsoft

代码编辑器：崇高文本3

Answer 1

一个简单的错误--您已经编写了getElementByID，而应该有getElementById。(这将立即显示在浏览器的开发工具控制台中。)

然后，您需要给step()打一次电话来启动它。

​

var canvas = document.getElementById('myCanvas');
var ctx = canvas.getContext('2d');

let screenWidth = 1000;
let screenHeight = 500;

class GameCharacter {
  constructor(x, y, width, height, color) {
    this.x = x;
    this.y = y;
    this.width = width;
    this.height = height;
    this.color = color;
  }
}

var blueSquare = new GameCharacter(
  50, 50, 50, 50, "rgb(0, 0, 255)"
);
var rectangle = new GameCharacter(
  75, 75, 100, 50, "rgb(0, 255, 0)"
);
var redSquare = new GameCharacter(
  100, 50, 50, 50, "rgb(255, 0, 0)"
);

var draw = function() {
  ctx.clearRect(0, 0, screenWidth, screenHeight);

  ctx.fillStyle = "rgb(0, 0, 255)";
  ctx.fillRect(blueSquare.x, blueSquare.y, blueSquare.width, blueSquare.height);

  ctx.fillStyle = rectangle.color;
  ctx.fillRect(rectangle.x, rectangle.y, rectangle.width, rectangle.height);

  ctx.fillStyle = redSquare.color;
  ctx.fillRect(redSquare.x, redSquare.y, redSquare.width, redSquare.height);

}

var step = function() {
  draw();

  window.requestAnimationFrame(step);
}

step();

canvas {
  border: 4px solid green;
  background-color: yellow;
}

<canvas id='myCanvas' width='1000' height='500'></canvas>

​