画布+ Dojo：getContext 未定义
当我在 IE7/WinXP32 中执行下面的代码时，控制台中的输出是“未定义”。当我进行以下两项修改中的任意一项时，输出将更改为预期的“getContext()”：
- 删除图像标签。
- 我使用：
知道这是怎么回事吗？解决方法可能是什么？
<!DOCTYPE HTML PUBLIC
"-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>Canvas</title>
<script type="text/javascript">
var djConfig = {parseOnLoad: false, isDebug: true};
</script>
<script type="text/javascript"
src="/development/javascript/dojo-release-1.4.3-src/dojo/dojo.js">
</script>
<!--[if IE]>
<script type="text/javascript" src="/javascript/excanvas_r73.js"></script>
<![endif]-->
<script type="text/javascript">
function draw() {
var canvas = dojo.byId("canvas");
console.log(canvas.getContext);
}
dojo.addOnLoad(draw);
</script>
</head>
<body>
<canvas id="canvas" width="100" height="100"></canvas>
<img src="nonexisting.gif">
</body>
</html>
更新：似乎替换“dojo.addOnLoad(draw);”用下面的代码就可以了。
function init() {
dojo.addOnLoad(draw);
}
if (dojo.isIE) {
dojo.connect('onload', init);
} else {
init();
}
When I execute the code below in IE7/WinXP32, then the output in the console is "undefined". The output changes to the expected "getContext()", when I make either of two modifications:
- I remove the image tag.
- I use: <body onload="draw()">
Any idea what is going on here? What may be a workaround?
<!DOCTYPE HTML PUBLIC
"-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>Canvas</title>
<script type="text/javascript">
var djConfig = {parseOnLoad: false, isDebug: true};
</script>
<script type="text/javascript"
src="/development/javascript/dojo-release-1.4.3-src/dojo/dojo.js">
</script>
<!--[if IE]>
<script type="text/javascript" src="/javascript/excanvas_r73.js"></script>
<![endif]-->
<script type="text/javascript">
function draw() {
var canvas = dojo.byId("canvas");
console.log(canvas.getContext);
}
dojo.addOnLoad(draw);
</script>
</head>
<body>
<canvas id="canvas" width="100" height="100"></canvas>
<img src="nonexisting.gif">
</body>
</html>
Update: Seems like replacing "dojo.addOnLoad(draw);" with the following code does the trick.
function init() {
dojo.addOnLoad(draw);
}
if (dojo.isIE) {
dojo.connect('onload', init);
} else {
init();
}
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评论（1）
dojo.addOnLoad 在 document.onload 之前触发。我认为它与 DOMContentLoaded 相关。也许 excanvas 在同一事件上进行初始化？你可以只使用 document.onload 吗？
dojo.addOnLoad fires before document.onload. I think it's associated with DOMContentLoaded. Perhaps excanvas does its initialization on the same event? Can you just use document.onload?