Firebase database running number

hello World,

i would like to ask how to generate running member id during member registration automatically if using firebase?

example : if member A register, firebase besides create unique ID, there’s no member id : 001 unless manually key in,

if 10 members register, 10 members will have member id from 001, 002, 003, 004, 005 automatically assigned

can firebase do auto increment? or do we need to set in at TS?