3. Stacked chart

<!DOCTYPE html>

<head>
    <meta charset="utf-8">
    <script src="https://d3js.org/d3.v4.min.js"></script>
    <style>
        body {
            margin: 0;
            position: fixed;
            top: 0;
            right: 0;
            bottom: 0;
            left: 0;
        }
        
        svg {
            font: 10px sans-serif;
        }
        
        .line {
            fill: none;
            stroke: black;
            stroke-width: 2px;
            .area {
                fill: lightsteelblue;
            }
        }

</style>
</head>

<body>
    <script>
        var margin = {
                top: 40,
                right: 40,
                bottom: 40,
                left: 40
            },
            width = 500, //interieur
            height = 300; //interieur

var x = d3.scaleTime().range([0, width]),
            y = d3.scaleLinear().range([height, 0]), // MODIF
            c = d3.scaleOrdinal(d3.schemeCategory10);

//https://www.d3noob.org/2013/01/filling-area-under-graph.html
        var area = d3.area() //MODIF
            .x(function(d) {
                return x(d.data.date)
            })
            .y0(function(d) {
                return y(d[0])
            }) 
            .y1(function(d) {
                return y(d[1])
            });

d3.text('stocks.csv', function(error, raw) {

var dsv = d3.dsvFormat(',')
            var data = dsv.parse(raw);

// Nest stock values by dates.
            var nested_data = d3.nest()
                .key(function(d) {
                    return d.date; // MODIF
                })
                .entries(data);

// Parse and caculate some values for each nested_data
            nested_data.forEach(function(s) {
                s.values.forEach(function(d) {
                    s.date = d3.timeParse("%b %Y")(d.date);
                    s[d.symbol] = +d.price
                });

s.maxPrice = d3.max(s.values, function(d) {
                    return d.price;
                });
                s.sumPrice = d3.sum(s.values, function(d) {
                    return d.price;
                });
            });
            
            
            // MODIF
            var stack = d3.stack()
                .keys(["MSFT", "AMZN", "IBM", "AAPL"])
                .order(d3.stackOrderNone)
                .offset(d3.stackOffsetNone);

// Create the default x-domain.
            x.domain(d3.extent(nested_data, function(d) {
                return d.date;
            }));

//MODIF Create the default y-domain.
            var nested_data_by_company = d3.nest()
                .key(function(d) {
                    return d.symbol; // MODIF
                })
                .entries(data);

nested_data_by_company.forEach(function(s) {
                s.values.forEach(function(d) {
                    d.date = d3.timeParse("%b %Y")(d.date);
                    d.price = +d.price;
                });

s.maxPrice = d3.max(s.values, function(d) {
                    return d.price;
                });
                s.sumPrice = d3.sum(s.values, function(d) {
                    return d.price;
                });
            });
            y.domain([0, d3.sum(nested_data_by_company.map(function(d) {
                return d.maxPrice;
            }))])

// Create the container "svg" and 1 subcontainer "g" for margins.
            var svg = d3.select("body").append("svg")
                .attr("width", width + margin.left + margin.right)
                .attr("height", height + margin.top + margin.bottom)
                .append("g")
                .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

//MODIF From the subcontainer "g", create 4 subsubcontainer "g" for each graph. 
            var g = svg.selectAll("g").data(stack(nested_data)).enter() //MODIF
                .append("g")

//MODIF Create a path for the area.
            g.append("path")
                .attr("class", "symbols")
                .attr("d", function(d) {
                    console.log(d)
                    return area(d);
                })
                .style("fill", function(d) {
                    return c(d.index) //MODIF
                })

// Display last value.
            g.append("text")
                .text(function(d, i) {
                    return d.key;
                })
                .attr("y", function(d) {
                    return height - (d[d.length - 1][0] + d[d.length - 1][1]) / 2
                })
                .attr("x", width + 2)
                .style("font-family", "monospace");
        });
    </script>
</body>

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