<canvas id="canvas" width="100" height="100"></canvas>
<script>
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var canvas2 = document.createElement('canvas');
canvas2.width = 20;
canvas2.height = 20;
var ctx2 = canvas2.getContext('2d');
ctx2.fillStyle = '#00f';
ctx2.fillRect(0, 0, 10, 10);
ctx2.fillStyle = '#0f0';
ctx2.fillRect(0, 10, 10, 10);
ctx2.fillStyle = '#f00';
ctx2.fillRect(10, 0, 10, 10);
ctx2.fillStyle = '#ff0';
ctx2.fillRect(10, 10, 10, 10);
var pattern = ctx.createPattern(canvas2, 'repeat');
ctx.fillStyle = pattern;
ctx.fillRect(0, 0, canvas.width, canvas.height);
ctx.fillStyle = '#f0f';
ctx.fillRect(40, 40, 20, 20);
</script>