D3 Examples - d3 Ex1 again

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<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v4.min.js"></script>
  <style>
    body { margin:0;position:fixed;top:0;right:0;bottom:0;left:10px; }
    svg {
      width: 100%;
      height: 100%;
    }
  </style>
</head>
​
<body>
  <svg></svg>
  <script>
    var city = 'San Francisco';
    var width = 800;
    var height = 300;
    var margin = {top: 20, bottom: 20, left: 20, right: 20};
    
    // dataset of city temperatures across time
    d3.tsv('data.tsv', (err, data) => {
      // clean the data
      data.forEach(d => {
        d.date = d3.timeParse("%Y%m%d")(d.date);
        d.date = new Date(d.date); // x
        d[city] = ++d[city]; // y
      });
    
      // scales
      var xExtent = d3.extent(data, d => d.date);
      var xScale = d3.scaleTime()
        .domain(xExtent)
        .range([margin.left, width - margin.right]);
      var yExtent = d3.extent(data, d => d[city]);
      var yScale = d3.scaleLinear()
        .domain(yExtent)
        .range([height - margin.bottom, margin.top]);
            var heightScale = d3.scaleLinear()
        .domain(yExtent)
        .range([0, height - margin.top - margin.bottom]);
​
      // create the rectangles
      var svg = d3.select('svg');
      
      var rect = svg.selectAll('rect')
        .data(data)
        .enter().append('rect')
        .attr('width', 5)
        .attr('height', function(d) {return heightScale(d[city])})
        .attr('x', function(d) { return xScale(d.date)})
        .attr('y', function(d) { return yScale(d[city])})
        .attr('fill', 'red')
        .attr('stroke', 'blue')
      
      // define axes
      
      var xAxis = d3.axisBottom()
        .scale(xScale);
      var yAxis = d3.axisLeft()
        .scale(yScale);
      
      svg.append('g')
        .attr('transform', 'translate(' + [0, height - margin.bottom ]+')')
        .call(xAxis)
      svg.append('g')
        .attr('transform', 'translate(' + [margin.left, 0] + ')')
        .call(yAxis);
​
    });
  </script>
</body>
​
    