Question : Find position of second to last period in a string

How do I take a string and remove the part of the string before the second to last period (including that period and if it exists).

Example
"abc.efg.ggg.this.part" returns "this.part"
"this.part" returns "this.part"
"f.this.part" returns "this.part"
"f.f.f.f.this.part" returns "this.part"

Answer : Find position of second to last period in a string

var s='abc.efg.ggg.this.part';
document.write(s.split(".").slice(-2).join("."));