<!DOCTYPE html>
<html>
<body>
<canvas id="output" width="100" height="100"></canvas>
<script>
var canvas = document.getElementById('output');
var ctx = canvas.getContext('2d');

const g = ctx.createConicGradient(3*Math.PI/2, 30, 30);
g.addColorStop(0, "#f0f");
g.addColorStop(0.25, "#0ff");
g.addColorStop(0.50, "#ff0");
g.addColorStop(0.75, "#f0f");
ctx.fillStyle = g;
ctx.fillRect(0, 0, 100, 100);
</script>
</body>
</html>