Help with variable in a loop

I am trying to pass the text from an input text box to a sender variable called variables. The first line of code works fine, but how do I make it dynamic so I can use a loop to load the “first” names into variables.first1, variables.first2, etc.

This works great…

variables.first1 = this[“first”+i+"_txt"].text;

But when I try to make the left side of the statement dynamic, it does not work.

this[“variables.first”+i] = this[“first”+i+"_txt"].text;

Any help would be appreciated.

Thanks,
John