我正在关注javascript / coffeescript / canvas教程，我有以下javascript代码:
(function() {
$(function() {
var canvas, context;
console.log("DOM is ready");
canvas = $('#myCanvas');
context = canvas.getContext('2d');
context.font = '40pt Calibri';
context.fillStyle = 'blue';
return context.fillText('Hello World!', 150, 100);
});
}).call(this);
在调用
canvas.getContext()时，我得到了Uncaught TypeError: undefined is not a function.如果我将
canvas = $('#myCanvas');替换为document.getElementById('myCanvas');，则效果很好。您认为出了什么问题？谢谢!!
有关信息，这是我的HTML:
<!doctype html>
<html>
<head>
<meta charset="utf-8" />
<title>Demo</title>
<script src="jquery-1.11.1.js"></script>
<script src="test.js"></script>
</head>
<body>
<canvas id="myCanvas" width="578" height="200"></canvas>
</body>
</html>
还有我的原始Coffeescript:
$ ->
console.log("DOM is ready")
canvas = document.getElementById('myCanvas');
context = canvas.getContext('2d')
context.font = '40pt Calibri';
context.fillStyle = 'blue';
context.fillText('Hello World!', 150, 100);
最佳答案
不同之处在于$('＃myCanvas')返回jQuery对象，而document.getElementById('myCanvas')返回canvas html元素。要获取 Canvas 上下文，您需要的不是元素。如果要使用jQuery，只需更改“canvas = $('＃myCanvas');”改为“ Canvas = $('＃myCanvas')[0];”