Making a grouped bar chart using d3.js

var svg = d3.select("svg"),
margin = {top: 20, right: 20, bottom: 30, left: 40},
width = +svg.attr("width") - margin.left - margin.right, height = +svg.attr("height") - margin.top - margin.bottom;

var x = d3.scaleBand().rangeRound([0,
width]).padding(0.1),
  y = d3.scaleLinear().rangeRound([height, 0]);

var g = svg.append("g")
.attr("transform", "translate(" + margin.left + "," + margin.top + ")");

var data = [
        {"Group":"Mars","count":10,"months":"June"},
        {"Group":"Jupiter","count":50,"months":"June"},
 {"Group":"Mars","count":70,"months":"July"},
        {"Group":"Jupiter","count":60,"months":"July"}];


     var ymaxdomain=d3.max(d,function(d){return d.count;});
     x.domain(d.map(function(d) {return d.months}));
    y.domain([0,ymaxdomain]);

   
  
   var x1=d3.scaleBand().rangeRound([0, x.bandwidth()]);
         x1.domain(d.map(function(d) {return d.months;}));

   

    g.selectAll(".bar")
        .data(data)
        .enter().append("rect")
        .attr("x", function(d,i) {console.log(d,i); return (x(d.months))}
        .attr("y", function(d) {return y(d.count); })
        .attr("width",x1.bandwidth())
        .attr("height", function(d) { return height - y(d.count); })
    
  g.append("g")
   .attr("class", "axis")
   .attr("transform", "translate(0," + height + ")")
   .call(d3.axisBottom(x));


  g.append("g")
   .attr("class", "axis")
   .call(d3.axisLeft(y).ticks(null, "s"))
   .append("text")
   .attr("x", 2)
   .attr("y", y(y.ticks().pop()) + 0.5)
   .attr("dy", "0.32em")
   .attr("fill", "#000")
   .attr("font-weight", "bold")
   .attr("text-anchor", "start")
   .text("count");

<style>

.bar {
  fill: steelblue;
  stroke:black
}

</style>

<!DOCTYPE html>
<svg width="600" height="600"></svg>
<body><script src="//d3js.org/d3.v4.min.js"></script></body>