Write a function isEven() which takes a single numeric argument and returns true if the number is even, and false otherwise
isEven(4); //true
isEven(21); //false
isEven(68); //true
isEven(333); //false
write a function factorial() which takes a single numeric argument and returns the factorial of that number
factorial(5); //120
factorial(2); //2
factorial(10); //3628800
factorial(0); //1
4! is 4 x 3 x 2 x 1
6! is 6 x 5 x 4 x 3 x 2 x 1
0! is 1
write a function kebabToSnake() which takes a single kebab-cased string argument and returns the snake_cased version.
kebabToSnake("hello-world"); //"hello_world"
kebabToSnake("dogs-are-awesome"); //"dogs_are_awesome"
kebabToSnake("blah"); //"blah"
Basically, replace "-"s with "_"s