This module implements a very simple message bus system for loose coupling of components. It is only used for logging initially, but we keep it in case there is a good reason for loose coupling, which may include communication between different instances. Messages are sent on a "bus" and any other module can subscribe to messages of certain types. The logger module is an example for a message consumer.
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Methods
on(type, fn) → {undefined}
Parameters:
| Name | Type | Description |
|---|---|---|
type |
string | String format "source:type" or only "type" for all handlers from any source. Request types should end in "-request", but I won't add code to check it. Handlers registered with on(...) should return a Promise - but I don't check that either. |
fn |
MessageHandlerCb |
This function is available on the MessageBusObj API-object returned by the createMessageBus function.
Note that if you call "on" more than once with the same callback function A, there will be no warning (no collision detection), and B, the callback will still be called just once.
Event types (examples)
Sent with msg={Error} from anywhere. Details are in the Error object.
[any]:error
Debug messages
[any]:info
Sent with msg={{type,hash}} whenever a new ONE microdata object has been saved to long-term storage. ´storage:new-object`
For example emitted by node-imap: alert(<string>message): Emitted when the server issues an
alert (e.g. "the server is going down for maintenance")
imap-mailbox-retriever:alert
Sent by an ImapMailboxRetriever instance after closing the IMAP connection
imap-mailbox-retriever:end
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Returns:
Type: undefined
once(type, fn) → {undefined}
Parameters:
| Name | Type | Description |
|---|---|---|
type |
string | String format "source:type" or only "type" for all handlers from any source. |
fn |
MessageHandlerCb |
This function is available on the MessageBusObj API-object returned by the createMessageBus function.
Note that unlike with "on", when you call "once" more than once with the same callback function A, just like with "on" there will be no warning, but B, unlike "on" the callback function will be called as many times as you called "once" to register it (albeit just once each time, of course).
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Returns:
Type: undefined
remove(type, fn) → {undefined}
Parameters:
| Name | Type | Description |
|---|---|---|
type |
string | |
fn |
MessageHandlerCb |
This function is available on the MessageBusObj API-object returned by the createMessageBus function.
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Returns:
Type: undefined
send(src, type, …messagesopt) → {undefined}
Parameters:
| Name | Type | Attributes | Description |
|---|---|---|---|
src |
string | ||
type |
string | ||
messages |
* |
<optional> <repeatable> |
This function is available on the MessageBusObj API-object returned by the createMessageBus function.
Listeners are called synchronously in insertion order - but all specific listeners, those who specified a source "source:type" in the .on(...) function, are called first. Listeners for handlers to be called regardless of the source are next.
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Returns:
Type: undefined
(static) createMessageBus(moduleId) → {MessageBusObj}
Parameters:
| Name | Type | Description |
|---|---|---|
moduleId |
string | A string used to identify the source of any messages sent through the returned MessageBus object's methods. |
Creates a MessageBus object associated with the given ID string.
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Returns:
An API-object that makes several functions available.
Type: MessageBusObj
(static) createWithRunningId(moduleId) → {MessageBusObj}
Parameters:
| Name | Type | Description |
|---|---|---|
moduleId |
string | A string used to identify the source of any messages sent through the returned MessageBus object's methods. Internally a counter is appended. |
Frontend to the createMessageBus function which
adds a number to the given moduleId string that increases by one each time the same
moduleId string is used. This function is for creating MessageBusObj instances for
modules that are not singletons. The created moduleId that can be used to subscribe to
messages from this component will be of the form ${moduleId}-${number}, for example, if
moduleId is myModule the actual ID associated with the MessageBusObj API-object
will be myModule-3 if this method is called three times with this same moduleId.
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Returns:
Type: MessageBusObj
(static) messageBusesIds() → {Array.<MessageBusObj>}
Creates and returns a cloned copy of the internal array of message bus IDs currently in use
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Returns:
Type: Array.<MessageBusObj>
Type Definitions
MessageHandlerCb(src, …messages) → {undefined}
Parameters:
| Name | Type | Attributes | Description |
|---|---|---|---|
src |
string | ||
messages |
* |
<repeatable> |
Callback function definition for message bus event handlers
Type definition:
(src: string, ...messages: unknown[]) => void
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Returns:
Returns undefined
Type: undefined