JS function: why this won't alert my greeting?

Question

I am curious why this won't alert my greeting. The code:

function myNameWelcome(userName, thought) {
  var greeting = "Welcome pardner, so your're name is " + userName + ". " + thought;
  return greeting;
}

myNameWelcome("Peter", "Shine on you crazy diamond.");

alert(greeting);

Answer 1

Your return value isn't being assigned to anything outside of the function.

Answer 2

greeting is out of scope. It was defined inside the function so it's not available at the scope you're calling alert(greeting);. Fixing this is easy:

var greeting;
function myNameWelcome(userName, thought) {
  greeting = "Welcome pardner, so your're name is " + userName + ". " + thought;
}

myNameWelcome("Peter", "Shine on you crazy diamond.");

alert(greeting);

or even better:

function myNameWelcome(userName, thought) {
  return "Welcome pardner, so your're name is " + userName + ". " + thought;
}

var greeting = myNameWelcome("Peter", "Shine on you crazy diamond.");

alert(greeting);

Answer 3

Because greeting is a local variable only accessible within myNameWelcome. It does not exist outside of the function.

See What is the scope of variables in JavaScript? to learn more about variable scope.