HTML5 动态创建 Canvas [英] HTML5 Dynamically create Canvas

问题描述

您好，我有一个关于使用 javascript 动态创建画布的问题.

Hi there I have a question about dynamically creating a canvas using javascript.

我创建了一个这样的画布:

I create a canvas like this:

var canvas = document.createElement('canvas');
canvas.id     = "CursorLayer";
canvas.width  = 1224;
canvas.height = 768;
canvas.style.zIndex   = 8;
canvas.style.position = "absolute";
canvas.style.border   = "1px solid";

但是当我尝试定位它时，我得到一个 null 值:

but when I try to locate it, I get a null value:

cursorLayer = document.getElementById("CursorLayer");

我做错了吗?有没有更好的方法来使用 JavaScript 创建画布?

Am I doing it wrong? Is there a better way to create a canvas using JavaScript?

推荐答案

问题是你没有在文档正文中插入画布元素.

The problem is that you do not insert your canvas element in the document body.

只需执行以下操作:

document.body.appendChild(canvas);

示例:

var canvas = document.createElement('canvas');

canvas.id = "CursorLayer";
canvas.width = 1224;
canvas.height = 768;
canvas.style.zIndex = 8;
canvas.style.position = "absolute";
canvas.style.border = "1px solid";


var body = document.getElementsByTagName("body")[0];
body.appendChild(canvas);

cursorLayer = document.getElementById("CursorLayer");

console.log(cursorLayer);

// below is optional

var ctx = canvas.getContext("2d");
ctx.fillStyle = "rgba(255, 0, 0, 0.2)";
ctx.fillRect(100, 100, 200, 200);
ctx.fillStyle = "rgba(0, 255, 0, 0.2)";
ctx.fillRect(150, 150, 200, 200);
ctx.fillStyle = "rgba(0, 0, 255, 0.2)";
ctx.fillRect(200, 50, 200, 200);

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