abksrv abksrv - 6 months ago 113
Javascript Question

Time axis in d3.js with specific time zone

I am using

d3.time.scale()
(reference here) to create time scale and providing tick values using
axis.tickValues([values])
(here). The ticks are rendered for the specified Date objects provided in [values].

All fine, but the tick values representations are always in current time zone of the browser. Now comes the requirement to show it in a specific time zone (say, 'Asia/Calcutta'). Is there a way to achieve this? The max option I see is for formatting the ticks, but not replacing them with custom values, which doesn't help the case.

EDIT: This might be achieved using an external library like moment.js, but it is preferred if this could be avoided.

Answer

Timezones are such a pain in the ass. But if you couple d3 with the the excellent moment timezone, this task becomes pretty easy with a tickformatter function:

// create reference to current zone
var currentTZ = "local";

// Define the axes
var xAxis = d3.svg.axis().scale(x)
  .orient("bottom").ticks(10)
  .tickFormat(function(d){
      console.log('format');
      if (currentTZ === "local")
        return moment(d).format('hh:mm:ss');
      else
        return moment(d).tz(currentTZ).format('hh:mm:ss');
  });

  // when user picks a new zone, re-draw axis
  ...
  .append("select")
  .on('change', function(d){
    currentTZ = this.options[ this.selectedIndex ].text;
    svg.selectAll("g.x.axis")
      .call(xAxis);
  })

Here's a full working example:

<!DOCTYPE html>
<html>

  <head>
    <meta charset="utf-8" />
    <script data-require="moment.js@2.10.2" data-semver="2.10.2" src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.10.2/moment.min.js"></script>
    <script data-require="moment-timezone-with-data@0.4.0" data-semver="0.4.0" src="http://momentjs.com/downloads/moment-timezone-with-data.js"></script>
    <style>
    /* set the CSS */
    
    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>
  </head>

  <body>
    <!-- load the d3.js library -->
    <script src="http://d3js.org/d3.v3.min.js"></script>
    <script>
    // Set the dimensions of the canvas / graph
    var margin = {
        top: 30,
        right: 20,
        bottom: 100,
        left: 50
      },
      width = 600 - margin.left - margin.right,
      height = 270 - margin.top - margin.bottom;

    var currentTZ = "local";

    // Set the ranges
    var x = d3.time.scale().range([0, width]);
    var y = d3.scale.linear().range([height, 0]);

    // Define the axes
    var xAxis = d3.svg.axis().scale(x)
      .orient("bottom").ticks(10)
      .tickFormat(function(d){
          console.log('format');
          if (currentTZ === "local")
            return moment(d).format('hh:mm:ss');
          else
            return moment(d).tz(currentTZ).format('hh:mm:ss');
      });

    var yAxis = d3.svg.axis().scale(y)
      .orient("left").ticks(5);

    // Define the line
    var valueline = d3.svg.line()
      .x(function(d) {
        return x(d.date);
      })
      .y(function(d) {
        return y(d.close);
      });

    // Adds the svg canvas
    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 + ")");

    var data = [{
      date: moment().add(0, 'hours').toDate(),
      close: Math.random() * 100
    }, {
      date: moment().add(1, 'hours').toDate(),
      close: Math.random() * 100
    }, {
      date: moment().add(2, 'hours').toDate(),
      close: Math.random() * 100
    }, {
      date: moment().add(3, 'hours').toDate(),
      close: Math.random() * 100
    }, {
      date: moment().add(4, 'hours').toDate(),
      close: Math.random() * 100
    }, {
      date: moment().add(5, 'hours').toDate(),
      close: Math.random() * 100
    }, {
      date: moment().add(6, 'hours').toDate(),
      close: Math.random() * 100
    }, {
      date: moment().add(7, 'hours').toDate(),
      close: Math.random() * 100
    }]

    // Scale the range of the data
    x.domain(d3.extent(data, function(d) {
      return d.date;
    }));
    y.domain([0, d3.max(data, function(d) {
      return d.close;
    })]);

    // Add the valueline path.
    svg.append("path")
      .attr("class", "line")
      .attr("d", valueline(data));

    // Add the X Axis
    svg.append("g")
      .attr("class", "x axis")
      .attr("transform", "translate(0," + height + ")")
      .call(xAxis)
      .selectAll("text")
      .style("text-anchor", "end")
      .attr("dx", "-.8em")
      .attr("dy", ".15em")
      .attr("transform", function(d) {
        return "rotate(-65)"
      });

    // Add the Y Axis
    svg.append("g")
      .attr("class", "y axis")
      .call(yAxis);
    
    d3.select("body")
      .append("select")
      .on('change', function(d){
        currentTZ = this.options[ this.selectedIndex ].text;
        svg.selectAll("g.x.axis")
          .call(xAxis)
          .selectAll("text")
          .style("text-anchor", "end")
          .attr("dx", "-.8em")
          .attr("dy", ".15em")
          .attr("transform", function(d) {
            return "rotate(-65)"
          });
      })
      .selectAll("option")
      .data(['local'].concat(moment.tz.names()))
      .enter()
      .append("option")
      .text(function(d){
        return d;
      });

  </script>
  </body>

</html>