Basically, variables and functions are both first-class citizens of javascript (http://en.wikipedia.org/wiki/First-class_citizen).  This means that you can't have a function and a variable with the same name in the same scope - there will be a conflict.  

In this case, @humphd is saying that declaring a variable called `isFriendly` (or the like), and then immediately afterwards defining a function called `isFriendly` makes the variable declaration redundant.