使用 javascript 将画布添加到页面

问题描述

我正在尝试使用 Javascript 将画布添加到原本没有画布的页面.我正在尝试执行以下操作:

I am trying to use Javascript in order to add a canvas to one page which originally does not have one. I am trying to do the following:

var canv=document.createElement("canvas");
canv.setAttribute("id", "canvasID");
alert(canv.id);
var c=document.getElementById("canvasID");
alert(c.id);

问题是第一个alert(canv.id) 结果是canvasID，而第二个alert 是未定义的，因为c 为null.

The problem is the the first alert(canv.id) results in canvasID, while the second alert is undefined because c is null.

谁能告诉我我做错了什么?

Can anybody tell me what am I doing wrong?

PS:代码设计为在 Greasemonkey 下运行，因此在 HTML 本身中添加画布及其 ID 不是一个可行的选择.

PS: the code is designed to run under Greasemonkey so adding the canvas and its ID in the HTML itself is not a viable option.

推荐答案

使用类似 Node.appendChild(child) 用于将其添加到 DOM:

Use something like Node.appendChild( child ) for adding it to the DOM:

var canv = document.createElement('canvas');
canv.id = 'someId';

document.body.appendChild(canv); // adds the canvas to the body element
document.getElementById('someBox').appendChild(canv); // adds the canvas to #someBox

<小时>

或者你可以使用element.innerHTML:

document.body.innerHTML += '<canvas id="someId"></canvas>'; // the += means we add this to the inner HTML of body
document.getElementById('someBox').innerHTML = '<canvas id="someId"></canvas>'; // replaces the inner HTML of #someBox to a canvas

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