JS异步编程系列一：用Jscex画圆_H5之家 - 中国HTML5教程资源分享第一站

关注老赵的jscex很久了，jscex利用eval(str)的无限可能，从“$async” 到“async”，从不支持if else 等到支持 if else等·，jscex正在不断完善和优化当中。jscex完全可以投入生产环境了··

昨天讲完pi,今天来画圆吧！

在支持html5的浏览器中执行下面代码：

XML/HTML Code复制内容到剪贴板

<!DOCTYPE HTML>
<html>
<body>
<canvas id="myCanvas" width="480" height="300" style="border:1px solid #c3c3c3;">
Your browser does not support the canvas element.
</canvas>
<script type="text/javascript">
var c = document.getElementById("myCanvas");
var ccxt = c.getContext("2d");
var x = 150;
var y = 150;
var r = 100;
cxt.moveTo(x - r, y);
for (var i = x - r; i < x + r + 1; i++) {
var tempY = Math.pow(r * r - (x - i) * (x - i), 1 / 2);
cxt.lineTo(i, y + tempY);
}
cxt.moveTo(x - r, y);
for (var i = x - r; i < x + r + 1; i++) {
var tempY = Math.pow(r * r - (x - i) * (x - i), 1 / 2);
cxt.lineTo(i, y - tempY);
}
cxt.stroke();
</script>
</body>
</html>

在Canvas里显示如下：

但是，我们明明是在画圆，怎么没有看到画圆的过程？javascript就是这样，解释完就画完了，而不会呈现解释的过程，这也是为什么javascript不用考虑多线程问题，仅仅UI线程。那么怎么看到画圆的过程？

jscex闪亮登场！

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<!DOCTYPE HTML>
<html>
<body>
<canvas id="myCanvas" width="480" height="300" style="border:1px solid #c3c3c3;">
Your browser does not support the canvas element.
</canvas>
<script language="javascript" type="text/javascript" src="lib/uglifyjs-parser.js"></script>
<script language="javascript" type="text/javascript" src="src/jscex.js"></script>
<script language="javascript" type="text/javascript" src="src/jscex.builderBase.js"></script>
<script language="javascript" type="text/javascript" src="src/jscex.async.js"></script>
<script type="text/javascript">
var c = document.getElementById("myCanvas");
var ccxt = c.getContext("2d");
var x = 150;
var y = 150;
var r = 100;
var drawAsync = eval(Jscex.compile("async", function () {
cxt.moveTo(x - r, y);
for (var i = x - r; i < x + r + 1; i++) {
$await(Jscex.Async.sleep(10));
var tempY = Math.pow(r * r - (x - i) * (x - i), 1 / 2);
cxt.lineTo(i, y + tempY);
cxt.stroke();
}
cxt.moveTo(x - r, y);
for (var i = x - r; i < x + r + 1; i++) {
$await(Jscex.Async.sleep(10));
var tempY = Math.pow(r * r - (x - i) * (x - i), 1 / 2);
cxt.lineTo(i, y - tempY);
cxt.stroke();
}
}));
drawAsync().start();
</script>
</body>
</html>

这样就可以目睹画圆全过程！