Spline

The Spline series is a point-line series with an automatic polynomial interpolation that produces smooth curves. This is simply a differently styled instance of PointLineAreaSeries.

// Creation of a spline series
const splineSeries = chart.addPointLineAreaSeries({ dataPattern: 'ProgressiveX' })
    .setAreaFillStyle(emptyFill)
    .setCurvePreprocessing({ type: 'spline' })

For "points" oriented guides, please refer to Scatter section.

Otherwise, the spline series functions exactly same as a Line series.

Also worth pointing out that it can also produce a Spline Area chart, simply by not disabling the area fill style as in above snippet.