• Update the chart when the browser window resizes.

• Savage label support (i.e. labels on bars or whatever).

• Horizontal and vertical lines. Probably will accept an array or single value that should bisect whatever axis.

  chart.horizontalLine([10, 20]);

• Gridlines.

• Legends.

• Layouts (different gridlines, axis positioning etc.).

• Tooltips.

• Click events and whatnot.

  chart.points({
    click: function (point) {
        console.log('Yo')
    }
  })
  

• Facets

  • Responsive if possible so they would stack on mobiles.
  • Support common and free scales.

• Update chart functions. Probably have .clearData(), .updateData() and .replaceData() functions.

• Transparent fill underneath lines.

• Points.
• Lines.
  • Group parameter in case you don't want different colours for each line.
• Area? Don't really like them because it's unclear if they're stacked or not.
• Columns (vertical bars).
• Stacked columns.
• Bars (horizontal columns).
• Stacked bars.
• Pie charts. May look at polar coordinates like ggplot.
• Error bars.

• Density plots.
• Histograms.
• Boxplots.

May have to apply some pre-transformation to the data. It could be like this:

const data = new Data(rawData)
chart(data.toDensity())
  .lines({fill: 'group'})

The user would have to then specify x and y, but that's a bit boilerplatey. To avoid that a parameter could be set by the Data class so that Chart will know to use whatever magic variables are generated. Alternatively there could be prebuilt functions like:

densityChart(rawData)

That and other special charts could extend Chart.