<canvas id="canvas" width="1024" height="600"></canvas>
<script type="text/JavaScript">
var ctx = document.getElementById('canvas').getContext('2d');
var gradient = ctx.createLinearGradient(0, 0, 300, 0);
gradient.addColorStop(0,"green");
gradient.addColorStop(1,"white");
ctx.fillStyle = gradient;
ctx.fillRect(10, 10, 300, 200);
</script>