Find the nth to last node in a linkedList

nthSll.js

function nthtoLast (SLL, n){
	if(SLL.head === null){
		return -1;
	}else{ 
		var len = 0,
		current = SLL.head; 
	
		while(current.next !== null){
			current = current.next;
			len ++ ;
		}
		if( n > len){
			return -1;
		}else{
		
		for(var i=0; i<=len-n+1; i++ ){
			temp = temp.next; 
		}
		return temp.value; 
		}
	}
}