macromedia flash flashcom:

Solved my own problem, here's an example:

function InvalidCredentialsException () {
this.message = "The username and password do not match any records in the
system.";
this.toString = function () {
return this.message;
};
}

try {
throw new InvalidCredentialsException();
} catch (e) {
if (e instanceof InvalidCredentialsException) {
...
}
}