D3 Examples - d3.js line graph with dual Y axes

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<!DOCTYPE html>
<meta charset="utf-8">
<style>
​
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;
}
​
</style>
<body>
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.17/d3.min.js"></script>
​
<script>
​
var margin = {top: 30, right: 40, bottom: 30, left: 50},
    width = 600 - margin.left - margin.right,
    height = 270 - margin.top - margin.bottom;
​
var parseDate = d3.time.format("%d-%b-%y").parse;
​
var x = d3.time.scale().range([0, width]);
var y0 = d3.scale.linear().range([height, 0]);
var y1 = d3.scale.linear().range([height, 0]);
​
var xAxis = d3.svg.axis().scale(x)
    .orient("bottom").ticks(5);
​
var yAxisLeft = d3.svg.axis().scale(y0)
    .orient("left").ticks(5);
​
var yAxisRight = d3.svg.axis().scale(y1)
    .orient("right").ticks(5); 
​
var valueline = d3.svg.line()
    .x(function(d) { return x(d.date); })
    .y(function(d) { return y0(d.close); });
    
var valueline2 = d3.svg.line()
    .x(function(d) { return x(d.date); })
    .y(function(d) { return y1(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
d3.csv("data2a.csv", function(error, data) {
    data.forEach(function(d) {
        d.date = parseDate(d.date);
        d.close = +d.close;
        d.open = +d.open;
    });
​
    // Scale the range of the data
    x.domain(d3.extent(data, function(d) { return d.date; }));
    y0.domain([0, d3.max(data, function(d) {
        return Math.max(d.close); })]); 
    y1.domain([0, d3.max(data, function(d) { 
        return Math.max(d.open); })]);
​
    svg.append("path")        // Add the valueline path.
        .attr("d", valueline(data));
​
    svg.append("path")        // Add the valueline2 path.
        .style("stroke", "red")
        .attr("d", valueline2(data));
​
    svg.append("g")            // Add the X Axis
        .attr("class", "x axis")
        .attr("transform", "translate(0," + height + ")")
        .call(xAxis);
​
    svg.append("g")
        .attr("class", "y axis")
        .style("fill", "steelblue")
        .call(yAxisLeft);   
​
    svg.append("g")             
        .attr("class", "y axis")    
        .attr("transform", "translate(" + width + " ,0)")   
        .style("fill", "red")       
        .call(yAxisRight);
​
});
​
</script>
</body>
​
    