What is mqemitter?
The 'mqemitter' npm package is a simple message queue emitter that allows you to publish and subscribe to messages. It is designed to be lightweight and easy to use, making it suitable for applications that require basic message queuing and event handling.
What are mqemitter's main functionalities?
Publishing Messages
This feature allows you to publish messages to a specific topic. The code sample demonstrates how to create an instance of MQEmitter and publish a message with a topic and payload.
const MQEmitter = require('mqemitter');
const emitter = MQEmitter();
emitter.emit({ topic: 'myTopic', payload: 'Hello, World!' }, (err) => {
if (err) {
console.error('Error publishing message:', err);
} else {
console.log('Message published successfully');
}
});
Subscribing to Messages
This feature allows you to subscribe to messages on a specific topic. The code sample shows how to set up a subscription to a topic and handle incoming messages.
const MQEmitter = require('mqemitter');
const emitter = MQEmitter();
emitter.on('myTopic', (message, cb) => {
console.log('Received message:', message.payload);
cb();
});
Unsubscribing from Messages
This feature allows you to unsubscribe from messages on a specific topic. The code sample demonstrates how to remove a previously set up subscription.
const MQEmitter = require('mqemitter');
const emitter = MQEmitter();
const handler = (message, cb) => {
console.log('Received message:', message.payload);
cb();
};
emitter.on('myTopic', handler);
// Later, to unsubscribe
emitter.removeListener('myTopic', handler);
Other packages similar to mqemitter
eventemitter3
EventEmitter3 is a high-performance event emitter for Node.js and the browser. It provides a similar publish/subscribe pattern but is more general-purpose and not specifically designed for message queuing.
redis
Redis is an in-memory data structure store that can be used as a message broker. It supports publish/subscribe messaging and offers more advanced features like persistence, clustering, and data structures.
mqtt
MQTT.js is a client library for the MQTT protocol, which is a lightweight messaging protocol designed for IoT. It provides more advanced features for message queuing and is suitable for applications requiring reliable message delivery.
MQEmitter
An Opinionated Message Queue with an emitter-style API, but with callbacks.
If you need a multi process MQEmitter, check out the table below:
Installation
npm install mqemitter
Examples
const mq = require('mqemitter')
const emitter = mq({ concurrency: 5 })
const message
emitter.on('hello world', function (message, cb) {
cb()
})
message = { topic: 'hello world', payload: 'or any other fields' }
emitter.emit(message, function () {
})
API
new MQEmitter ([options])
- options
<object>
concurrency
<boolean>
maximum number of concurrent messages that can be on concurrent delivery. Default: 0
wildcardOne
<string>
a char to use for matching exactly one non-empty level word. Default: +
wildcardSome
<string>
a char to use for matching multiple level wildcards. Default: #`matchEmptyLevels
<boolean>
If true then wildcardOne
also matches an empty word. Default: true
separator
<string>
a separator character to use for separating words. Default: /
Create a new MQEmitter class.
MQEmitter is the class and function exposed by this module.
It can be created by MQEmitter()
or using new MQEmitter()
.
For more information on wildcards, see this explanation or Qlobber.
emitter.emit (message, callback)
message
<object>
callback
<Function>
(error) => void
Emit the given message, which must have a topic
property, which can contain wildcards as defined on creation.
emitter.on (topic, listener, [callback])
topic
<string>
listener
<Function>
(message, done) => void
callback
<Function>
() => void
Add the given listener to the passed topic. Topic can contain wildcards, as defined on creation.
The listener
must never error and done
must not be called with an err
object.
callback
will be called when the event subscribe is done correctly.
emitter.removeListener (topic, listener, [callback])
The inverse of on
.
emitter.close (callback)
callback
<Function>
() => void
Close the given emitter. After, all writes will return an error.
Wildcards
MQEmitter supports the use of wildcards: every topic is splitted according to separator
.
The wildcard character +
matches exactly non-empty one word:
const mq = require('mqemitter')
const emitter = mq()
emitter.on('hello/+/world', function(message, cb) {
console.log(message)
cb()
}
emitter.on('hello/+', function(message, cb) {
console.log(message)
cb()
})
emitter.emit({ topic: 'hello/my/world', something: 'more' })
emitter.emit({ topic: 'hello//world', something: 'more' })
The wildcard character +
matches one word:
const mq = require('mqemitter')
const emitter = mq({ matchEmptyLevels: true })
emitter.on('hello/+/world', function(message, cb) {
console.log(message)
cb()
})
emitter.on('hello/+', function(message, cb) {
console.log(message)
cb()
})
emitter.emit({ topic: 'hello/my/world', something: 'more' })
emitter.emit({ topic: 'hello//world', something: 'more' })
The wildcard character #
matches zero or more words:
const mq = require('mqemitter')
const emitter = mq()
emitter.on('hello/#', function(message, cb) {
console.log(message)
cb()
})
emitter.on('#', function(message, cb) {
console.log(message)
cb()
})
emitter.on('hello/my/world/#', function(message, cb) {
console.log(message)
cb()
})
emitter.emit({ topic: 'hello/my/world', something: 'more' })
Of course, you can mix #
and +
in the same subscription.
LICENSE
MIT