<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>画布</title>
<script type="text/javascript">var canvas = document.getElementById("myCanvas");
if(canvas && canvas.getContext){
var cxt = canvas.getContext("2d");
cxt.fillStyle="#FF0000";
cxt.fillRect(0,0,200,150);
}
</script>
</head>//为什么没效果,换种方式就可以<body>
<canvas id="myCanvas" width="300" height="150" style="border:1px dashed #c3c3c3;">
</canvas>
</body>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>画布</title>
<script type="text/javascript">
function A(){
var canvas = document.getElementById("myCanvas");
if(canvas && canvas.getContext){
var cxt = canvas.getContext("2d");
cxt.fillStyle="#FF0000";
cxt.fillRect(0,0,200,150);
}
}
</script>
</head>//换这种方式就可以<body onload="javascript:A();">
<canvas id="myCanvas" width="300" height="150" style="border:1px dashed #c3c3c3;">
</canvas>
</body>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>画布</title>
<script type="text/javascript">var canvas = document.getElementById("myCanvas");
if(canvas && canvas.getContext){
var cxt = canvas.getContext("2d");
cxt.fillStyle="#FF0000";
cxt.fillRect(0,0,200,150);
}
</script>
</head>//为什么没效果,换种方式就可以<body>
<canvas id="myCanvas" width="300" height="150" style="border:1px dashed #c3c3c3;">
</canvas>
</body>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>画布</title>
<script type="text/javascript">
function A(){
var canvas = document.getElementById("myCanvas");
if(canvas && canvas.getContext){
var cxt = canvas.getContext("2d");
cxt.fillStyle="#FF0000";
cxt.fillRect(0,0,200,150);
}
}
</script>
</head>//换这种方式就可以<body onload="javascript:A();">
<canvas id="myCanvas" width="300" height="150" style="border:1px dashed #c3c3c3;">
</canvas>
</body>
</canvas>到这里 这个元素才被创建出来。 总之没有创建的元素时无法获取的。
要把script放在页面body下面,或者放到window.onload事件(页面加载完成后触发)中才可以