Proper way to draw gridlines

Assuming that you have Mike Bostock’s standard margins defined and you have defined a linear scale for the y-axis the following code will create horizontal gridlines without using tickSize().

svg.selectAll("line.horizontalGrid").data(yScale.ticks(4)).enter()
    .append("line")
        .attr(
        {
            "class":"horizontalGrid",
            "x1" : margin.right,
            "x2" : width,
            "y1" : function(d){ return yScale(d);},
            "y2" : function(d){ return yScale(d);},
            "fill" : "none",
            "shape-rendering" : "crispEdges",
            "stroke" : "black",
            "stroke-width" : "1px"
        });