code: function drawGridLines(){
              if (maskGridLines) {
                  svg.selectAll('.horizontal-grid-line').remove();
              }
              if (baseLine) {
                  svg.selectAll('.extended-x-line').remove();
              }
  
              maskGridLines = svg.select('.grid-lines-group')
                  .selectAll('line.horizontal-grid-line')
                  .data(yScale.ticks(yTicks))
                  .enter()
                    .append('line')
                      .attr('class', 'horizontal-grid-line')
                      .attr('x1', (xAxisPadding.left))
                      .attr('x2', chartWidth)
                      .attr('y1', (d) => yScale(d))
                      .attr('y2', (d) => yScale(d));
  
              if (baseLine) {
                  svg.selectAll('.extended-x-line').remove();
              }
  
              //draw a horizontal line to extend x-axis till the edges
              baseLine = svg.select('.grid-lines-group')
                  .selectAll('line.extended-x-line')
                  .data([0])
                  .enter()
                    .append('line')
                      .attr('class', 'extended-x-line')
                      .attr('x1', (xAxisPadding.left))
                      .attr('x2', chartWidth)
                      .attr('y1', chartHeight)
                      .attr('y2', chartHeight);
          }
docs: Draws grid lines on the background of the chart
  @return void