canvas 绘制二次贝塞尔曲线

代码：
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>canvas</title>
    <script>
        function init() {

            var canvas=document.getElementById('canvas');
            var ctx=canvas.getContext('2d');
            ctx.strokeStyle="dark";
            ctx.beginPath();
            ctx.moveTo(0,200);
            ctx.quadraticCurveTo(75,50,300,200);
            ctx.stroke();
            ctx.globalCompositeOperation="source-over";


            ctx.strokeStyle="blue";
            ctx.beginPath();
            ctx.moveTo(75,50);
            ctx.lineTo(0,200);
            ctx.moveTo(75,50);
            ctx.lineTo(300,200);
            ctx.stroke();

        }

    </script>
</head>
<body  onload="init();">
<canvas  id="canvas"  width="400"   height="400"></canvas>
</body>
</html>
　　效果：
2017-09-09 11:30:18