ActionScript 3.0 - Else If conditions for text field - if-statement

Question

I need to make an If/Else condition.
I make a form with Adobe Flash, at the first page, I need to make a login form. I want to make Input Text, but the input text must be filled. If the input text is empty, I want to make alert if the form must be filled. In my idea I have an input text called nama.text and in the bottom of the input text, I put a button called next.bt. Then, I put dynamic text "alert.text" in the bottom of the button.
My problem:
I want, if the button pressed by user with a filled input text, user will be direct to go to next frame. But, if the input text is empty, I want to make alert "Nama Must Be filled" and make user stay in this page and cannot go to next frame until the Nama.text is filled. I'm so sorry for my English, but I hope, everyone here understand with my questions.

Answer 1

"I want, if the button pressed by user with a filled input text, user
will be direct to go to next frame. But, if the input text is empty, i
want to make alert "Nama Must Be filled" and make user stay in this
page and cannot go to next frame until the Nama.text is filled"
(1) Don't ever use . (eg: fullstop) as part of a variable name. A fullstop means something else to the AS3 compiler. Generally it means "a property belonging to this variable". Maybe rename astxt_Nama?
(2) You can check the AS3 manual for Textfield options. One of them is a property called .length. This tells you how many chars exist inside your textfield.
So in your click function for handling Next button press:
if (txt_Nama.length <= 1) //if smaller or equal to 1
{
//if Smaller-than or Equal-to 1 then not enough chars typed
showTheAlert(); //tell AS3 to do this function
}
else
{
//if larger than 1 then something was typed
mc_Pages.gotoAndStop(2); //tells content MovieClip go to its frame 2
}
Then create a separate function to handle the display of alert (Don't put this function inside of another function)
function showTheAlert() :void
{
trace("No name was typed. Try again...");
//# Do something here like make some "warning" MClip visible
//maybe... mc_Alert.addChild;
//or... mc_Alert.visible = true;
}
(3) I suggest you create a MovieClip object to hold your content or pages. An MClip has its own timeline and go to its own frames like Stage. If you tell Stage to move to another frame then your code may not work
someMC.gotoAndStop(5); //# Correct... tells MovieClip to move frames. Code works because and MovieClip are on same Stage frame.
gotoAndStop(5); //# Wrong... tells Stage to move frames. Code only works on other frame where it is typed.