<canvas id="canvas"></canvas>
<script type="text/JavaScript">
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
ctx.save(); // save default state
ctx.fillStyle = "blue";
ctx.fillRect(20, 20, 100, 100);
ctx.restore(); // restore default state
ctx.fillRect(170, 80, 100, 100);
</script>