updating the posting from and to periods by 1 at the month

[SM14]

I am developing a bot in irpa which requires updating the from and to periods by 1. I wanted to develop a custom script but is showing incorrect can someone help me correct it?

var Valutabl;
for(var i = 0; i <$.s_ChangeViewPostingPeriodSp.fromper1>.; i++)
{
if($.s_ChangeViewPostingPeriodSp.fromper1[i]== "1")
{
$.s_ChangeViewPostingPeriodSp.fromper1[i]=='2';

}
}
Valutabl = s_ChangeViewPostingPeriodSp.fromper1;
return Valutabl;