function greetingForAllFriends(friends){
if(friends[index]!==null && friends!==null){
return("Hello, "+""+friends+"!")// ...
}
else {return null}}

say's index is not defined in the function???

addWord(array, string){
array.push(string)
array=this.array
}
gives
Test Passed: Value == ["hello"]
TypeError: Cannot call method 'push' of undefined
at addWord