private function methodExists(methodName:String) : Boolean
{
	var exists:Boolean;
	try {
		exists = this[methodName] != null;
	} catch (e:Error) {
		exists = false;
	} 
	return exists;
}

Just add a method like this in a Class that needs to call methods dynamically, without a prior knowledge of whether they exist or not.

Test if class method exists in Action Script

class

ActionScript 3