[D3] Build a Line Chart with D3 v4

Line charts are often used to plot temporal data, like a stock price over time. In this lesson we’ll see how to use D3 APIs to create our own simplified version of the charts seen on Google Finance.

var margin = {
top: 10,
right: 20,
bottom: 65,
left: 40
};
var width = 400 - margin.left - margin.right;
var height = 600 - margin.top - margin.bottom;

var svg = d3.select('.chart')
.append('svg')
.attr('width', width + margin.left + margin.right)
.attr('height', height + margin.top + margin.bottom)
.call(responsivefy)
.append('g')
.attr('transform', 'translate(' + margin.left + ', ' + margin.top + ')');

/**
* Load data
*/
d3.json('../data/data3.json', function (err, data) {
const parseTime = d3.timeParse('%Y/%m/%d');

data.forEach(company => {
company.values.forEach(d => {
d.date = parseTime(d.date)
d.close = +d.close
})
})

/**
* x axis
*/
const xScale = d3.scaleTime()
.domain([
d3.min(data, co => d3.min(co.values, d => d.date)),
d3.max(data, co => d3.max(co.values, d => d.date))
])
.range([0, width])
.nice();
svg.append('g')
.attr('transform', `translate(0, ${height})`)
.call(d3.axisBottom(xScale).tickSize(10).tickPadding(5))
.selectAll('text')
.attr('text-anchor', 'end')
.attr('transform', 'rotate(-45)');

/**
* Y axis
*/
const yScale = d3.scaleLinear()
.domain([
d3.min(data, co => d3.min(co.values, d => d.close)),
d3.max(data, co => d3.max(co.values, d => d.close))
])
.range([height, 0])
.nice();
svg.append('g')
.call(d3.axisLeft(yScale));

/**
* Create lines
*/
const line = d3.line()
.x(d => xScale(d.date))
.y(d => yScale(d.close))
.curve(d3.curveCatmullRom.alpha(0.5)); //smmoth the line

svg
.selectAll('.line')
.data(data)
.enter()
.append('path')
.attr('class', 'line')
.attr('d', d => line(d.values)) // draw the line
.style('stroke', (d, i) => ['#FF9900', '#3369E8'][i])
.style('stroke-width', 2)
.style('fill', 'none');
});

function responsivefy(svg) {
// get container + svg aspect ratio
var container = d3.select(svg.node().parentNode),
width = parseInt(svg.style("width")),
height = parseInt(svg.style("height")),
aspect = width / height;

// add viewBox and preserveAspectRatio properties,
// and call resize so that svg resizes on inital page load
svg.attr("viewBox", "0 0 " + width + " " + height)
.attr("preserveAspectRatio", "xMinYMid")
.call(resize);

// to register multiple listeners for same event type,
// you need to add namespace, i.e., 'click.foo'
// necessary if you call invoke this function for multiple svgs
// api docs: https://github.com/mbostock/d3/wiki/Selections#on d3.select(window).on("resize." + container.attr("id"), resize);

// get width of container and resize svg to fit it
function resize() {
var targetWidth = parseInt(container.style("width"));
svg.attr("width", targetWidth);
svg.attr("height", Math.round(targetWidth / aspect));
}
}