<canvas id="testCanvas" width="200" height="100" style="border:1px solid #d3d3d3;">
trình duyệt của bạn không hỗ trợ canvas</canvas>

<script>
var c = document.getElementById("testCanvas");
var ctx = c.getContext("2d");
ctx.beginPath();
ctx.arc(95,50,40,0,2*Math.PI);
ctx.stroke();
</script> 

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