D3 Examples - connect the dots

xxxxxxxxxx
 
<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v4.min.js"></script>
  <script src="data.js"></script>
  <script src="data2.js"></script>
  <style>
    body { margin:0;position:fixed;top:0;right:0;bottom:0;left:0; }
  </style>
</head>
​
<body>
  <script>
    
    const width = 960;
    const height = 500;
    const margin = { left: 40, right: 20, top: 20, bottom: 20};
    var svg = d3.select('body').append('svg')
      .attr('width', width)
      .attr('height', height)
​
    const t = d3.transition().duration(1000);
    
    const xScale = d3.scaleTime()
        .range([margin.left, width - margin.right])
    
    const yScale = d3.scaleLinear()
        .range([height - margin.bottom, margin.top ])
    
    
    const createLine = data => {
      console.log(data)
       const xExtent = d3.extent(data, d => d.time)
       const yExtent = d3.extent(data, d => d.change)
      xScale.domain(xExtent)
        yScale.domain(yExtent)
      
      let lines = svg.selectAll('line')
        .data(data, d => d.time)
​
      lines.exit().remove()
      
      const enter = lines.enter().append('line')
        .attr('x1', d => xScale(d.time))
        .attr('y1', d => yScale(d.change))
        .attr('x2', (d,i) => data[i + 1] ? xScale(data[i + 1].time) : xScale(d.time))
        .attr('y2', (d,i) => data[i + 1] ? yScale(data[i + 1].change) : yScale(d.change));
​
      lines = enter.merge(lines)
        .attr('stroke', 'black')
        .attr('stroke-width', 1)
        .transition(t)
        .attr('x1', d => xScale(d.time))
        .attr('y1', d => yScale(d.change))
        .attr('x2', (d,i) => data[i + 1] ? xScale(data[i + 1].time) : xScale(d.time))
        .attr('y2', (d,i) => data[i + 1] ? yScale(data[i + 1].change) : yScale(d.change));
    }
    
    const xAxis = d3.axisTop().scale(xScale);
    const yAxis = d3.axisLeft().scale(yScale);
​
    svg.append('g')
      .attr('transform', `translate(0, ${margin.top})`)
      .call(xAxis);
​
    svg.append('g')
      .attr('transform', `translate(${margin.left}, 0)`)
      .call(yAxis);
    
    let index = 0;
    
    data1.forEach(d => {
        d.change = +d.change;
        d.rate = +d.rate;
      });
    
    createLine(data1)
    setTimeout(() => {
      data2.forEach(d => {
        d.change = +d.change;
        d.rate = +d.rate;
      });
        createLine(data2);
      
    }, 3000)
  </script>
</body>
​
    