barPadding (barPadding) {
        if (!arguments.length) {
            return this._rangeBandPadding();
        }
        this._rangeBandPadding(barPadding);
        this._gap = undefined;
        return this;
    }
Get or set the spacing between bars as a fraction of bar size. Valid values are between 0-1.
Setting this value will also remove any previously set {@link BarChart#gap gap}. See the
{@link https://github.com/d3/d3-scale/blob/master/README.md#scaleBand d3 docs}
for a visual description of how the padding is applied.
@param {Number} [barPadding=0]
@returns {Number|BarChart}