---
title: Writing message handlers
card_id: 9950
modified: yes
---

# Writing message handlers

When you write a handler for a message, you specify a sequence of statements for HyperCard to run. Each message handler has the following form, with the italicized words as placeholders:

```
on [ph:messageName]
    [ph:statements]
end [ph:messageName]
```

When it runs the message handler, HyperCard sends each line of the handler as a message itself (so handlers can call other handlers).

<b>Important</b>: The message name does <i>not</i> have to be one of HyperCard’s built-in system messages or commands.

For example, if you wanted a new command called `doubleBeep` that would beep twice, you would write a handler for it as follows:

```
on doubleBeep
   beep
   beep
end doubleBeep
```

Of course, HyperCard doesn’t know about the `doubleBeep` command, so it will never be sent automatically in response to an event. But you can send `doubleBeep` from the Message box or use it as a statement in other handlers.

For example, the script of a card button might contain the following handler for the system message `mouseUp`:

```
on mouseUp
  doubleBeep
end mouseUp
```

If the script also contains the `doubleBeep` handler (or if the script of any object later in the message-passing path contains it), the `mouseUp` message will send the `doubleBeep` message, and `doubleBeep` will send two `beep` commands. Because `beep` is a built-in command, HyperCard beeps twice.

If HyperCard can’t find the `doubleBeep` message, it will complain (with a dialog box) that it “can’t understand” the message.

## Related Topics

* [Handling messages](/HyperTalkReference/hypertalkbasics/Handling-messages)
* [on](/HyperTalkReference/keywords/on)
* [The message-passing order](/HyperTalkReference/hypertalkbasics/The-message-passing-order)
* [Using parameter variables](/HyperTalkReference/hypertalkbasics/Using-parameter-variables)
* [What are messages?](/HyperTalkReference/hypertalkbasics/What-are-messages)