Brush and Zoom 2

<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v5.min.js"></script>
  <style>
  
    .line {
        fill: none;
        stroke: steelblue;
        stroke-width: 1.5px;
    }
  .zoom {
    cursor: move;
    fill: none;
    pointer-events: all;
  }
  </style>
</head>

<body>
  <svg width="873" height="500"></svg>
  <script>
    
    //Brush and zoom based off:
    //https://bl.ocks.org/EfratVil/92f894ac0ba265192411e73f633a3e2f
    
    var data = [];
    //var data = [{"depthNum":0,"depth":4},{"depthNum":1,"depth":8},{"depthNum":2,"depth":10},{"depthNum":3,"depth":11},{"depthNum":4,"depth":15},{"depthNum":5,"depth":19},{"depthNum":6,"depth":22},{"depthNum":7,"depth":23},{"depthNum":8,"depth":30}];
    var innerHeight=607;
    var innerWidth=250;
    var svg = d3.select("svg");
    var margin = {top: 20, right: 20, bottom: 110, left: 40};
    var margin2 = {top: 436, right: 20, bottom: 30, left: 40};
    var width = +svg.attr("width") - margin.left - margin.right;
    var width2 = +svg.attr("width") - margin2.left - margin2.right;
    var height = +svg.attr("height") - margin.top - margin.bottom;
    var height2 = +svg.attr("height") - margin2.top - margin2.bottom;

//from developer.mozilla.org
    function getRandomArbitrary(min, max) {
  		return Math.random() * (max - min) + min;
	}
    
		function genPoints(j){
      var data = [];
      var ranMin = 0;
      var ranMax = 2000;
      for(i=0;i<j;i++)
        {
          var ranDep = getRandomArbitrary(ranMin,ranMax);
          data.push(
          {
            "depthNum":i,
            "depth":ranDep
          }
          );
          
        }
      render(data);
    }
    
    
    var xScale = d3.scaleLinear().range([0, width]);
    var xScale2 = d3.scaleLinear().range([0, width]);
    var yScale = d3.scaleLinear().range([height, 0]);
    var yScale2 = d3.scaleLinear().range([height2, 0]);
    
    //console.log(xScale);
    
    var xAxis = d3.axisBottom(xScale),
    xAxis2 = d3.axisBottom(xScale2),
    yAxis = d3.axisLeft(yScale),
    yAxis2 = d3.axisLeft(yScale2);
    
    var brush = d3.brushX()
      .extent([[0, 0], [width, height2]])
      .on("brush end", brushed);

var zoom = d3.zoom()
      .scaleExtent([1, Infinity])
      .translateExtent([[0, 0], [width, height]])
      .extent([[0, 0], [width, height]])
      .on("zoom", zoomed);
    
     var line = d3.line()
        .x(function (d) { return xScale(d.depthNum); })
        .y(function (d) { return yScale(d.depth); });

var line2 = d3.line()
        .x(function (d) { return xScale2(d.depthNum); })
        .y(function (d) { return yScale2(d.depth); });
    
    var clip = svg.append("defs").append("svg:clipPath")
        .attr("id", "clip")
        .append("svg:rect")
        .attr("width", width)
        .attr("height", height)
        .attr("x", 0)
        .attr("y", 0);

var Line_chart = svg.append("g")
        .attr("class", "focus")
        .attr("transform", "translate(" + margin.left + "," + margin.top + ")")
        .attr("clip-path", "url(#clip)");

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

var context = svg.append("g")
        .attr("class", "context")
        .attr("transform", "translate(" + margin2.left + "," + margin2.top + ")");
    
    function render(data){
  xScale.domain(d3.extent(data, function(d) { return d.depthNum; }));
  yScale.domain([0, d3.max(data, function (d) { return d.depth; })]);
  xScale2.domain(xScale.domain());
  yScale2.domain(yScale.domain());

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

focus.append("g")
        .attr("class", "axis axis--y")
        .call(yAxis);

Line_chart.append("path")
        .datum(data)
        .attr("class", "line")
        .attr("d", line);

context.append("path")
        .datum(data)
        .attr("class", "line")
        .attr("d", line2);

context.append("g")
      .attr("class", "axis axis--x")
      .attr("transform", "translate(0," + height2 + ")")
      .call(xAxis2);

context.append("g")
      .attr("class", "brush")
      .call(brush)
      .call(brush.move, xScale.range());

svg.append("rect")
      .attr("class", "zoom")
      .attr("width", width)
      .attr("height", height)
      .attr("transform", "translate(" + margin.left + "," + margin.top + ")")
      .call(zoom);
    }
    genPoints(100);
    
    function brushed() {
      if (d3.event.sourceEvent && d3.event.sourceEvent.type === "zoom") return; // ignore brush-by-zoom
      var s = d3.event.selection || xScale2.range();
      xScale.domain(s.map(xScale2.invert, xScale2));
      Line_chart.select(".line").attr("d", line);
      focus.select(".axis--x").call(xAxis);
      svg.select(".zoom").call(zoom.transform, d3.zoomIdentity
          .scale(width / (s[1] - s[0]))
          .translate(-s[0], 0));
    }

function zoomed() {
      if (d3.event.sourceEvent && d3.event.sourceEvent.type === "brush") return; // ignore zoom-by-brush
      var t = d3.event.transform;
      xScale.domain(t.rescaleX(xScale2).domain());
      Line_chart.select(".line").attr("d", line);
      focus.select(".axis--x").call(xAxis);
      context.select(".brush").call(brush.move, xScale.range().map(t.invertX, t));
    }
    
    //genLine(10);
    //console.log(data);
    
    
    
  </script>
</body>

https://d3js.org/d3.v5.min.js