DyGraphs is a decent Javascript library to plot time series data points.

I chose DyGraphs a long time ago mainly due to its small footprint of 123530 bytes for dygraph.2.0.0.min.js

One of the things it allows you to do now is to add a different plotter algorithm to plot data. One such example can be found on the demo page is that of a BarChart plotter. If you look at the code it is a fairly small addition.

One of the possible plots missing though is a PieChart. It happened that I needed a PieChart for my project and I did not want to switch to E.g. ChartJS [ Release 2.5.0 ] so I wrote my own little PieChart function for DyGraphs.

function pieChartPlotter ( e ) {
        var ctx  = e.drawingContext;
        var self = e.dygraph.user_attrs_.myCtx;
        var itm, nme, data = self._pieData;
        if ( ! data )  {
          var t, i, y, all, total = 0;
          data = {};
          all = e.allSeriesPoints; // array of array
          for ( t=0; t

The one thing you will see in this code is that I calculate the required PieChart data once and then check for its existance each time I enter this function. This is requried beause DyGraph does currently not call the plotter function in a context but rather in the global browser context ( I.e. the this object is the browser Window ).

So instead I ‘added’ ( read hacked ) myCtx to the dygraphs – plotter options to gain access to my local JavaScript object where I buffer the _pieData.

While this may not be the nicest pie chart around, it is a small, basic function which can be expanded on fairly easily.

Addendum: Here is how to use this code

    this._options  = {
      labels: ["Date","Count"],
      legend: 'always',
      title:  "  ",
      myCtx: this,
      animatedZooms: true,
      hideOverlayOnMouseOut: false,
      stackedGraph: false,
      clickCallback    : this.onGraphClicked,
      showRangeSelector: true,
      underlayCallback : this.highlightWeekend,
      legendFormatter  : this.legendFormatter,
      highlightSeriesOpts : {
        strokeWidth: 3,
        strokeBorderWidth: 1,
        highlightCircleSize: 5
      }
    };
    this._chart = new Dygraph ( dom, this._data.data, this._options );
    ...