A word limit all dynamic text input boxes in flash allow only numbers to be entered

The dynamic is just beginning with the following:
function Limittonum () {
if (This.text!= "-" && isNaN (This.text)) {
This.text = ';
}
}
a_txt.onchanged = Limittonum;
b_txt.onchanged = Limittonum;
c_txt.onchanged = Limittonum;
... Found a little cumbersome, suddenly remembered ' prototype ':
TextField.prototype.onChanged = function () {
if (This.text!= "-" && isNaN (This.text)) {
This.text = ';
}
This limits all dynamic text entry boxes in Flash.
This can also be inferred. Like what:
MovieClip.prototype.onPress = StartDrag;
MovieClip.prototype.onRelease = Stopdrag;
MovieClip.prototype.onReleaseOutside = Stopdrag; all clip clips in Flash can be dragged and pulled.
:) enjoy!