simple D3 line chart

copied from: https://leanpub.com/D3-Tips-and-Tricks/read#leanpub-auto-starting-with-a-basic-graph

by gdicerbo

HTML

<body></body>

CSS

body {
    font: 12px Arial;
}
path {
    stroke: steelblue;
    stroke-width: 2;
    fill: none;
}
.axis path, .axis line {
    fill: none;
    stroke: grey;
    stroke-width: 1;
    shape-rendering: crispEdges;
}
.area {
    fill: lightsteelblue;
    stroke-width: 0;
}
.area1 {
    fill: red;
    stroke-width: 0;
}

JavaScript

var margin = {
    top: 30,
    right: 20,
    bottom: 30,
    left: 50
};
var width = 600 - margin.left - margin.right;
var height = 270 - margin.top - margin.bottom;

var parseDate = d3.time.format("%Y").parse;

var x = d3.time.scale().range([0, width]);
var y = d3.scale.linear().range([height, 0]);

var xAxis = d3.svg.axis().scale(x)
    .orient("bottom").ticks(5);

var yAxis = d3.svg.axis().scale(y)
    .orient("left").ticks(5);

var area = d3.svg.area()
    .x(function(d) { return x(d.date); })
    .y0(height)
    .y1(function(d) { return y(d.close); });
 
 var area1 = d3.svg.area()
    .x(function(d) { return x(d.date); })
    .y0(height)
    .y1(function(d) { return y(d.open); });

var valueline = d3.svg.line()
    .x(function (d) {
      return x(d.date);
    })
    .y(function (d) {
      return y(d.close);
    });

var valueline2 = d3.svg.line()
    .x(function(d) { return x(d.date); })
    .y(function(d) { return y(d.open); });

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 + ")");

// Get the data
var data = [{
    date: "2018",
    close: "0",
    open: "0"
}, {
    date: "2019",
    close: "2242378",
    open: "38"
}, {
    date: "2020",
    close: "67.00",
    open: "45"
}, {
    date: "2021",
    close: "89.70",
    open: "22"
}, {
    date: "2022",
    close: "99.00",
    open: "32"
}];

data.forEach(function (d) {
    d.date = parseDate(d.date);
    d.close = +d.close;
});

// Scale the range of the data
x.domain(d3.extent(data, function (d) {
    return d.date;
    }));
y.domain([0, d3.max(data, function (d) {
    return d.close;
    })]);

svg.append("path")
        .datum(data)
        .attr("class", "area")
        .attr("d", area);

svg.append("path")
        .datum(data)
        .attr("class", "area1")
        .attr("d",...