Need help with setting setting a variable only if it doesnt exist already.

[dumbnoob]

Ok, I have a script, that when run, will cycle through the contents of an array, and when it reaches the end, will loop back to the beginning.

 

However, if the variable used to determine its position has not been set on the page already, it doesn't run.

 

I need a way to set the variable, only if it does not exist.

 

My code below

 

javascript: 

if (confpos==undefined){
confpos=0;
} 

config=[1,2,4,7,12,16];
IT=(config[confpos]);
  
  alert (IT);

confpos=++confpos; 
IT=(config[confpos]); 

if (IT==undefined){
confpos=1;
} 
void(0);

 

If I have previously punched

 

 javascript: confpos=0;  void(0); 

 

into my address bar, the code will run fine, but, I need it to do what it's meant to, without me having to predefine confpos. In that, if confpos isn't set, then I need it to set it automatically, so that it will be able to run the rest of the script.