D3 Interactive Line Chart

<!DOCTYPE html>
<meta charset="utf-8">
<style>

.line {
  fill: none;
  stroke: steelblue;
  stroke-width: 1.5px;
}

</style>

var parseTime = d3.timeParse("%Y%m%d");

d3.tsv("data.tsv", type, function(error, data) {
  if (error) throw error;

var cities = data.columns.slice(1).map(function(id) {
    return {
      id: id,
      values: data.map(function(d) {
        return {date: d.date, temperature: d[id]};
      })
    };
  });

var svg = d3.select("svg").call(d3.zoom().on("zoom", zoomed)),
    margin = {top: 20, right: 80, bottom: 30, left: 50},
    width = svg.attr("width") - margin.left - margin.right,
    height = svg.attr("height") - margin.top - margin.bottom,
    g = svg.append("g").attr("transform", "translate(" + margin.left + "," + margin.top + ")");

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

var line = d3.line()
    .curve(d3.curveBasis)
    .x(function(d) { return x(d.date); })
    .y(function(d) { return y(d.temperature); });

var zoom = d3.zoom()
    .scaleExtent([1 / 4, 8])
    .translateExtent([[-width, -Infinity], [2*width, Infinity]])
    .extent([[0, 0], [width, height]])
    .on("zoom", zoomed);

x.domain(d3.extent(data, function(d) { return d.date; }));

y.domain([
    d3.min(cities, function(c) { return d3.min(c.values, function(d) { return d.temperature; }); }),
    d3.max(cities, function(c) { return d3.max(c.values, function(d) { return d.temperature; }); })
  ]);

var xAxis = d3.axisBottom(x);
  var yAxis = d3.axisLeft(y);

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

var mY = g.append("g")
    .attr("class", "axis axis--y")
    .call(yAxis);

z.domain(cities.map(function(c) { return c.id; }));

var city = g.selectAll(".city")
    .data(cities)
    .enter().append("g")
      .attr("class", "city");

city.append("path")
      .attr("class", "line")
      .attr("d", function(d) { return line(d.values); })
      .style("stroke", function(d) { return z(d.id); })
      .attr("id", function(d) { return d.id.substring(0,3).toUpperCase() })
      .style("opacity", 1);

city.append("text")
      .datum(function(d) { return {id: d.id, value: d.values[d.values.length - 1]}; })   	
      .attr("transform", function(d) { return "translate(" + x(d.value.date) + "," + y(d.value.temperature) + ")"; })
      .attr("x", 3)
      .attr("dy", "0.35em")
      .style("font", "10px sans-serif")
      .text(function(d) { return d.id; })
      .on("click", function() {
        var ID = d3.select(this).text().substring(0,3).toUpperCase();
        if(svg.select("path#" + ID).style("opacity") == 1) {
          svg.select("path#" + ID).style("opacity", 0);
        } else {
          svg.select("path#" + ID).style("opacity", 1);
        }
      })
      .on("mouseover", function() {
        var ID = d3.select(this).text().substring(0,3).toUpperCase();
        if(svg.select("path#" + ID).style("opacity") != 0) {
          svg.selectAll("path").each(function(d, i) { 
              if(d != null) {
                var newID = d.id.substring(0,3).toUpperCase();
                if(svg.select("path#" + newID).style("opacity") == 0) {
                  svg.select("path#" + newID).style("opacity", 0);
                }
                if(svg.select("path#" + newID).style("opacity") == 1) {
                  svg.select("path#" + newID).style("opacity", 0.1);
                }
              }
            });
          svg.select("path#" + ID).style("opacity", 1);
        }
      })
      .on("mouseout", function() {
          var ID = d3.select(this).text().substring(0,3).toUpperCase();
          svg.selectAll("path").each(function(d, i) { 
            if(d != null) {
              var ID = d.id.substring(0,3).toUpperCase();
              if(svg.select("path#" + ID).style("opacity") == 0.1) {
                svg.select("path#" + ID).style("opacity", 1);
              }
              if(svg.select("path#" + ID).style("opacity") == 0) {
                svg.select("path#" + ID).style("opacity", 0);
              }
            }
          });
      })

function zoomed() {
    svg.selectAll(".city").attr("transform", d3.event.transform);
    d3.selectAll('.line').style("stroke-width", 2/d3.event.transform.k);
    mX.call(xAxis.scale(d3.event.transform.rescaleX(x)));
    mY.call(yAxis.scale(d3.event.transform.rescaleY(y)));
  }

});

function type(d, _, columns) {
  d.date = parseTime(d.date);
  for (var i = 1, n = columns.length, c; i < n; ++i) d[c = columns[i]] = +d[c];
  return d;
}

</script>

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