var x = d3.scaleTime()
    .domain([new Date(2010, 7, 1), new Date(2012, 7, 1)])
    .range([0, width]);

var xAxis = d3.axisBottom(x)
    .ticks(d3.timeYear);

g.append("g")
    .attr("transform", "translate(0," + height + ")")
    .call(customXAxis);