Scatter plot brushing

Scatter plot brushing.

<!DOCTYPE html>
<meta charset="utf-8">

for (i = 0; i < samples; i++) {
             data.push({
                 x: random(),
                 y: random()
             });
         }
         return data;
     }

var ds = randomData(300);
 
     var margin = { top: 20, right: 20, bottom: 30, left: 50 };
     width = 800 - margin.left - margin.right,
     height = 400 - margin.top - margin.bottom;
     
     var x = d3.scaleLinear()
         .range([0, width]);

var y = d3.scaleLinear()
         .range([height, 0]);

var xAxis = d3.axisBottom(x).ticks(12),
         yAxis = d3.axisLeft(y).ticks(12 * height / width);

var svg = d3.select("#g1").append("svg")
              .attr("id", "g1_svg")
              .attr("data-margin-right", margin.right)
              .attr("data-margin-left", margin.left)
              .attr("data-margin-top", margin.top)
              .attr("data-margin-bottom", margin.bottom)
              .attr("width", width + margin.left + margin.right)
              .attr("height", height + margin.top + margin.bottom)
              .append("g")
              .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

x.domain(d3.extent(ds, function (d) { return d.x; })).nice();
     y.domain(d3.extent(ds, function (d) { return d.y; })).nice();

svg.append("g")
     .attr("class", "x axis ")
     .attr('id', "axis--x")
     .attr("transform", "translate(0," + height + ")")
     .call(xAxis);

svg.append("g")
         .attr("class", "y axis")
         .attr('id', "axis--y")
         .call(yAxis);

var dot = svg.selectAll(".dot")
         .data(ds)
       .enter().append("circle")
         .attr("class", "dot")
         .attr("r", 5)
         .attr("cx", function (d) { return x(d.x); })
         .attr("cy", function (d) { return y(d.y); })
         .attr("opacity", 0.7)
         .style("fill", "#4292c6");

svg.append("g")
      .call(d3.brush().extent([[0, 0], [width, height]]).on("brush", brushed).on("end", brushended));

function brushed() {
         var s = d3.event.selection,
             x0 = s[0][0],
             y0 = s[0][1],
             dx = s[1][0] - x0,
             dy = s[1][1] - y0;
         // console.log(s);

svg.selectAll('circle')
            .style("fill", function (d) {
                if (x(d.x) >= x0 && x(d.x) <= x0 + dx && y(d.y) >= y0 && y(d.y) <= y0 + dy)
                     { return "#ec7014"; }
                else { return "#4292c6"; }
            });
     }

function brushended() {
         if (!d3.event.selection) {
             svg.selectAll('circle')
               .transition()
               .duration(150)
               .ease(d3.easeLinear)
               .style("fill", "#4292c6");
         }
     }
   
</script>
</body>

https://d3js.org/d3.v4.min.js