我在页面底部加载Javascript文件(excanvas)时无法正常工作 [英] Javascript file (excanvas) not working when I load it at the bottom of the page
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问题描述
这有效:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<script src="/js/msgv/widgets/excanvas2.js" type="text/javascript"></script>
<script type="text/javascript" charset="utf-8">
function canvasTest(){
console.log("beginning canvasTest");
var b_canvas = document.getElementById("regularCanvas");
var b_context = b_canvas.getContext("2d");
b_context.fillRect(50, 25, 150, 100);
}
</script>
</head>
<body onLoad="canvasTest()">
<canvas id="regularCanvas" style="border: 1px dotted; float: left;" class="clear" height="225" width="300"></canvas>
</body>
</html>
这不是:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
两者之间的唯一区别是我在页面中的加载位置.当我在脑海中装载exanvas时，一切正常.将其加载到主体底部时会出现错误.
The only difference between the two is where I'm loading it in the page. Everything works fine when I load excanvas in the head. I get an error when I load it at the bottom of the body.
<script type="text/javascript" charset="utf-8">
function canvasTest(){
console.log("beginning canvasTest");
var b_canvas = document.getElementById("regularCanvas");
var b_context = b_canvas.getContext("2d");
b_context.fillRect(50, 25, 150, 100);
}
</script>
</head>
<body onLoad="canvasTest()">
<canvas id="regularCanvas" style="border: 1px dotted; float: left;" class="clear" height="225" width="300"></canvas>
<script src="/js/msgv/widgets/excanvas2.js" type="text/javascript"></script>
</body>
</html>
推荐答案
RTFM :
在标记中出现canvas元素之前，必须在页面中包含excanvas.js文件.这是由于IE中的限制所致，我们需要在IE在标记中看到任何实例之前做一些魔术.建议将其放在头部.
The excanvas.js file must be included in the page before any occurrences of canvas elements in the markup. This is due to limitations in IE and we need to do our magic before IE sees any instance of in the markup. It is recommended to put it in the head.
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