draw canvas diagonal
<!DOCTYPE html><html><body><script>
var canvas = document.createElement('canvas');
canvas.width = 100;
canvas.height = 100;
var ctx = canvas.getContext('2d');
ctx.strokeStyle = 'black';
ctx.beginPath();
ctx.moveTo(0, 0);
ctx.lineTo(100, 100);
ctx.lineWidth = 1;
ctx.stroke();
document.body.appendChild(canvas);
</script></body></html>