為什么我照著3-1課程打，最后畫圓仍然最后畫圓仍然畫不出來。
代碼供上，請大神指教
time.html
<!DOCTYPE html>
<html>
<head>
?<meta charset="UTF-8">
?<title>Document</title>
?<script type="text/javascript" src="clock.js"></script>
?<style type="text/css">
??div{
???text-align: center;
???margin-top: 250px;
??}
??#clock{
???border: 1px solid #ccc;
??}
?</style>
</head>
<body>
?<div>
??<canvas id="clock" height="200px" width="200px"></canvas>
?</div>
?</body>
</html>
clock.js
var dom = document.getElementById('clock');
var ctx = dom.getContext('2d');
var width = ctx.canvas.width;
var height = ctx.canvas.height;
var r = width / 2;
function drawBackground() {
?"use strict";
?ctx.translate(r, r);
?ctx.beginPath();
?ctx.arc(0, 0, r, 0, 2 * Math.PI, false);
?ctx.stroke();
}drawBackground();
2017-10-24
?<script type="text/javascript" src="clock.js"></script> ? 這句要放到body中div的后邊
2017-03-03
<script>
clock.js
var dom = document.getElementById('clock');
var ctx = dom.getContext('2d');
var width = ctx.canvas.width;
var height = ctx.canvas.height;
var r = width / 2;
function drawBackground() {
?"use strict";
?ctx.translate(r, r);
?ctx.beginPath();
?ctx.arc(0, 0, r, 0, 2 * Math.PI, false);
?ctx.stroke();
}
drawBackground();
</script>
加一個(gè)<script></script>就可出來啊