interpolate (interpolate) {
        logger.warnOnce('dc.lineChart.interpolate has been deprecated since version 3.0 use dc.lineChart.curve instead');
        if (!arguments.length) {
            return this._interpolate;
        }
        this._interpolate = interpolate;
        return this;
    }
Gets or sets the interpolator to use for lines drawn, by string name, allowing e.g. step
functions, splines, and cubic interpolation.

Possible values are: 'linear', 'linear-closed', 'step', 'step-before', 'step-after', 'basis',
'basis-open', 'basis-closed', 'bundle', 'cardinal', 'cardinal-open', 'cardinal-closed', and
'monotone'.

This function exists for backward compatibility. Use {@link LineChart#curve}
which is generic and provides more options.
Value set through `.curve` takes precedence over `.interpolate` and `.tension`.
@deprecated since version 3.0 use {@link LineChart#curve} instead
@see {@link LineChart#curve}
@param  {d3.curve} [interpolate=d3.curveLinear]
@returns {d3.curve|LineChart}