How to draw gridlines

[richardumesh]

Hi, Iam looking to show some gridlines when i load the sketchpad. something like this

I used the below function to draw the grid. but the lines disapper as soon i start writing on the sketchpad
drawGrid(ctx, w, h, step) {
// ctx.beginPath();
ctx.beginPath();
for (var y = 0; y <= h; y += step) {
ctx.moveTo(0, y);
ctx.lineTo(w, y);
}
// set the color of the line
ctx.strokeStyle = 'rgb(20,20,20)';
// just for fun
ctx.lineWidth = 1;
// for your original question - you need to stroke only once
ctx.stroke();

}