javascript check and replace two strings

Question

I have two strings str1 and str2 . Check both of them and see if any one string is empty.

If yes, then replace that str with another one.

if(indexOf(str1) < -1 || indexOf(str2) < -1){
   str1 = str2;
 }

will this work?

Answer 1

No, that won't work for numerous reasons. This will though:

if(!str1)
    str1 = str2;
else if(!str2)
    str2 = str1;