axis.tickFormat()

axis.tickFormat([format])

If format is specified, sets the tick format function and returns the axis. If format is not specified, returns the current format function, which defaults to null. A null format indicates that the scale’s default formatter should be used, which is generated by calling scale.tickFormat. In this case, the arguments specified by axis.tickArguments are likewise passed to scale.tickFormat.

See d3-format and d3-time-format for help creating formatters. For example, to display integers with comma-grouping for thousands:

axis.tickFormat(d3.format(",.0f"));

More commonly, a format specifier is passed to axis.ticks:

axis.ticks(10, ",f");

This has the advantage of setting the format precision automatically based on the tick interval.