chart.xAxis(...).outerTickSize is not a function code example
Example: remove axis tick ends d3
axis.tickSizeOuter(0) // (d3 version 4.x) & (d3 version 5.x)
axis.outerTickSize(0) // (d3 version 3.x)
axis.tickSizeOuter(0) // (d3 version 4.x) & (d3 version 5.x)
axis.outerTickSize(0) // (d3 version 3.x)