Why did logging a result of a function returns undefined?

There's something bugging my mind recently and sorry for the bad title. Assume I create a little snippet.

Code:

[panda=js]function pushArray(arr, str)
 arr.push(str);
}

Let's assume that someone was currently using my snippet. He pushes a certain value into an array and blah.

Code:

[panda=js]var blah = [1];
var push = pushArray(blah, 2);

Now he wants to check the value of the variable [ic]push[/ic]. But sadly it returns [ic]undefined[/ic].

Code:

[panda=js]// pushArray module code here
// his code here
console.log(push); // returns undefined

I think you'd understand what I mean now.
I need an answer; why did it always returns undefined unless there's a [ic]return[/ic] statement behind the code inside the function?

What you're attempting would look something like this. ( everything in the same scope )

Code:

[panda=js](function() {

  function pushArray(arr, str) {
    arr.push(str);
    return arr;
  };
 
  var blah = [1],
      push = pushArray(blah, 2);

  console.log(push); // [1, 2]

})();

The reason push is undefined is because you're not assigning a value to it, you're only calling the function. To assign a value with your function you need to return arr, which returns blah + the newly added value.

Super. Just what I needed. Thank you very much.

Topic solved and archived.