<!DOCTYPE html>
<html>
<body>
<canvas id ="output" width="300" height="400"></canvas>
<script>
var canvas = document.getElementById('output');
var ctx = canvas.getContext('2d');

ctx.beginPath();
ctx.roundRect(10, 10, 100, 100, [20]);
ctx.fill();
</script>
</body>
</html>

