Just things

<!DOCTYPE html>
<body>
    <script src="https://d3js.org/d3.v5.min.js"></script>
    <script>
        var m = 40, w = 960 - m*2, h = 500 - m*2;
        var svg = d3.select('body').append('svg')
            .attr('width', w + m*2).attr('height', h + m*2)
            .append('g')
            .attr('transform', 'translate(' + [m,m] + ')');

var data = [];
        for (var i = 0; i< 50; i++) {
            data.push({
                index: i + '',
                value: Math.floor(Math.random() * 10),
                radius: Math.floor(Math.random() * 3)
            });
        }

data.forEach(function(d) {
            d.index = +d.index;
        })

var color = d3.scaleOrdinal(d3.schemeSet2);
        
        lineChart(data)
        barChart(data);

function lineChart(data) {
            var lineChart = svg.append('g')
                .attr('class', 'lineChart');

var lineW = w/2 - m;
            
            var x = d3.scaleLinear()
                .range([0,lineW]);
            var y = d3.scaleLinear()
                .range([h,0]);
            var radius = d3.scaleLinear()
                .range([5,10]);

var line = d3.line()
                .x((d,i) => x(i))
                .y((d) => y(d.value));

//x.domain([-5,data.length]);

x.domain([0, d3.max(data, (d) => d.index)])
            y.domain([0,d3.max(data,(d,i) => d.value)])
            radius.domain(d3.extent(data,(d) => d.radius));

lineChart.append('g')
                .attr('class', 'y-axis')
                .attr('transform', 'translate(' + x(0) + ',0)')
                .call(d3.axisLeft(y))
            lineChart.append('g')
                .attr('class', 'x-axis')
                .attr('transform', 'translate(0,' + h + ')')
                .call(d3.axisBottom(x))

lineChart.append('path')
                .data([data])
                .attr('d', line)
                .attr('fill', 'none')
                .attr('stroke', 'black')
                .attr('stroke-width', 3)

lineChart.selectAll('.circle')
                .data(data)
                .enter().append('circle')
                .attr('class', 'circle')
                .attr('cx', (d) => x(d.index))
                .attr('cy', function(d,i) { return y(d.value); })
                .attr('r', (d) => radius(d.radius))
                .attr('fill', 'white')
                .attr('stroke', (d) => color(d.radius))
                .attr('stroke-width', 5)
            		.on('mouseover', function(a,b,c) {
                  var rects = d3.selectAll('.rect')._groups[0];
              		d3.select(rects[a.radius]).style('opacity', 0.7);
            		})
            		.on('mouseout', function(a,b,c) {
                  d3.selectAll('.rect').style('opacity', 1);
            		})
        }

function barChart(data) {
            var barW = w/2 - m;
            var barChart = svg.append('g')
                .attr('class', 'barChart')
                .attr('transform', 'translate(' + (barW + m) + ',0)');

var nest = d3.nest()
                .key((d) => d.radius)
                .sortKeys(d3.ascending)
                .entries(data);

var y = d3.scaleLinear()
                .range([h,0])
                .domain([0,d3.max(nest, (d) => d.values.length)]);

var x = d3.scaleBand()
                .range([0,barW])
                .domain(nest.map((d) => d.key))
                .padding(.2);

barChart.append('g')
                .attr('transform', 'translate(0,' + h + ')')
                .call(d3.axisBottom(x))

barChart.selectAll('rect')
                .data(nest)
                .enter().append('rect')
            		.attr('class', 'rect')
                .attr('x', (d) => x(d.key))
                .attr('y', (d) => y(d.values.length))
                .attr('width', x.bandwidth())
                .attr('height', (d) => h - y(d.values.length))
                .attr('fill', (d) => color(d.key))
        }
    </script>
</body>

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