How to get keyCode from input TextField?

programming flash
1

**I want to detect which keys are pressed while user input text into TextField.
I tried something like
**
import flash.text.TextFormat;
import flash.text.TextField;
import flash.events.Event;
import flash.events.KeyboardEvent;

 txt:TextField = new TextField;
 txt.type = TextFieldType.INPUT;
 txt.background = false;
 txt.border = false;
 txt.multiline = false;
 txt.width = 226;
 txt.height = 36;
 txt.maxChars  = 17;

 var txt_format:TextFormat = new TextFormat ();
 txt_format.font="Impact";
 txt_format.size=36;
 txt_format.color=0xFFB000;
 txt_format.align="left"
 txt_format.leftMargin=15;
 
  txt.setTextFormat (txt_format);
  addChild(txt);

txt.addEventListener (KeyboardEvent.KEY_DOWN, keyDownHandler);

function keyDownHandler (event:KeyboardEvent):void
{

trace (event.keyCode);}

**but this doesn’t work.

I am quite beginner in as3, so if anyone can show me where I made mistake, and how to make it works? Thanks**