How do you start a function without a button?

Question

I currently have an action that starts with a button click. But I want it to start on frame 1 automatically without a button. How do I need to edit my code to make this work correctly? It's a typewriter effect and I plan on exporting it out as a .MOV and importing it into Adobe Premiere. I also need to figure out how to get the background transparent if possible. Thanks in advance!
Here is what I have.
Button to start the action
btn.onRelease = function()
    txt_ani.startTypeEffect();
Typewriter function
typewriter effect
// clear the string
//txt.text = "";
// stop the page
stop();
// the text string
// use \n for line breaks
var _txt:String = "“This is the text that will start after you press the button, but hopefully it will start automatically soon”";
var _tmr:Number; // timer
var _sec:Number = 62; // milliseconds till next letter
var i:Number = 1;
var l:Number = _txt.length;
function TypeEffect() : Void
    if( i < l )
        txt.text = _txt.substr( 0, i );
        i++;
    } else {
        txt.text = _txt;
        clearInterval( _tmr );
        trace("\t< FIN >");
    //trace( i );
// call this function to start:
function startTypeEffect() : Void
    trace("\t< START >");
    _tmr = setInterval( TypeEffect, _sec );

Answer 1

My movie has 1 frame. I deleted the layer that had the button, so I have an AS layer with the following code in it.
txt_ani.startTypeEffect();
And a layer below it with my movie clip with the Function code on one layer and the text in another layer below it.
When I do play it, nothing happens. But when I add some frames to the movie, it starts after a delay, but I keep seeing "START" in my output tab due to the Trace I have, which makes the text appear very quickly. I think I may need some code to stop it from restarting.
Where should this code you provided be put? And do I need additional code to have the text not speed up?