manasi s,

Indeed, in the examples, bar chart does not support negative values.

To do so, you have to change the yScale configuration as follows :

this.yScale
.range([this.barHeight, 0])
.domain(d3.extent(this.data, d => d[this.valueField])
.nice();

The d3.extent() method returns an array containing the bounds of your datasource ( this.data ).