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https://github.com/flipeador/js-eventemitter
Store listener functions and emit events.
https://github.com/flipeador/js-eventemitter
async-await browser event-emitter javascript nodejs
Last synced: 14 days ago
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Store listener functions and emit events.
- Host: GitHub
- URL: https://github.com/flipeador/js-eventemitter
- Owner: flipeador
- License: apache-2.0
- Created: 2023-08-17T21:36:19.000Z (over 1 year ago)
- Default Branch: v2.0
- Last Pushed: 2024-07-05T23:48:05.000Z (7 months ago)
- Last Synced: 2024-11-14T18:25:42.902Z (2 months ago)
- Topics: async-await, browser, event-emitter, javascript, nodejs
- Language: JavaScript
- Homepage:
- Size: 15.6 KB
- Stars: 0
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
README
# EventEmitter
Store listener functions and emit events.
Similar to [Node.js - Class: EventEmitter][node-ee].
## Installation
Install from Git repository:
```
npm i flipeador/js-eventemitter#semver:^2.0.0
```
You may also install just from the subdirectory:
```
pnpm i "flipeador/js-eventemitter#path:src&semver:^2.0.0"
```
It is recommended to install from the subdirectory if your package manager supports it.
## Examples
Synchronous listener functions
```js
import { EventEmitter } from '@flipeador/js-eventemitter';
const ee = new EventEmitter();
ee.on('message', () => {
console.log('message #1');
return 'value #1';
});
ee.on('message', () => {
console.log('message #2');
throw new Error('error #2'); // (1)
});
ee.on('message', async () => {
console.log('message #3'); // (2)
return 'value #3';
});
// By default, listener functions exceptions are thrown immediately.
// This stops the loop and subsequent listener functions will not be called.
try {
ee.emit('message', ['arg1', 'arg2']);
} catch (error) {
// Note that "message #3" (2) is not displayed.
console.log('[CATCH]', error.message); // (1)
}
// Separator.
console.log('-'.repeat(50));
// The above behavior can be changed by specifying an error handler.
// The return value of the error handler is added as a result.
console.log(ee.emit('message', [], error => error));
```
```
message #1
message #2
[CATCH] error #2
--------------------------------------------------
message #1
message #2
message #3
[
'value #1',
Error: error #2
...,
Promise { }
]
```
Asynchronous listener functions
```js
import { EventEmitter } from '@flipeador/js-eventemitter';
const ee = new EventEmitter();
ee.on('message', () => {
console.log('message #1');
return 'value #1';
});
ee.on('message', async () => {
console.log('message #2');
throw new Error('error #2'); // (1)
});
ee.on('message', async () => {
console.log('message #3'); // (2)
return 'value #3';
});
try {
// In async functions, exceptions are not thrown immediately.
// This allows 'message #3' (2) to be displayed on the console.
const results = ee.emit('message', ['arg1', 'arg2']);
await Promise.all(results ?? []); // throws (1)
} catch (error) {
console.log('[CATCH]', error.message); // (1)
}
// Separator.
console.log('-'.repeat(50));
// Note that 'value #3' is no longer a promise.
let results = ee.emit('message', [], error => error);
results = await Promise.allSettled(results ?? []);
results = results.map(result => result.reason ?? result.value);
console.log(results);
```
```
message #1
message #2
message #3
[CATCH] error #2
--------------------------------------------------
message #1
message #2
message #3
[
'value #1',
Error: error #2
...,
'value #3'
]
```
Access results from previous listeners
```js
import { EventEmitter } from '@flipeador/js-eventemitter';
const ee = new EventEmitter();
ee.on('message', async function() {
return new Promise(resolve => { // (1)
setTimeout(
() => resolve('message #1'),
3000
);
});
});
ee.on('message', async function() {
// Get the result of the previous listener.
const result = this.results.at(-1);
// Returns a promise that resolves after the previous (1).
return result.then(() => 'message #2'); // (2)
});
const results = ee.emit('message');
await results[1]; // wait for (2)
console.log(results);
```
```js
[ Promise { 'message #1' }, Promise { 'message #2' } ]
```
Valid event names and maximum number of listeners
```js
import { EventEmitter } from '@flipeador/js-eventemitter';
const MAX_LISTENERS = 10; // default
const ee = new EventEmitter(
// List of valid event names.
'message'
);
// Set the maximum number of listeners.
ee.setMaxListeners(MAX_LISTENERS);
try {
// Emit an invalid event.
ee.on('exit', console.log);
} catch (error) {
console.log('[CATCH]', error);
}
// Add more than the maximum number of listeners.
for (let n = MAX_LISTENERS+1; n; --n)
ee.on('message', console.log);
```
```
[CATCH] EventEmitterError: Invalid event name
... {
event: 'exit'
}
(node:12580) Error: Possible memory leak detected: 11 listeners added to message
(Use `node --trace-warnings ...` to show where the warning was created)
```
## License
This project is licensed under the **GNU General Public License v3.0**.
See the [license file](LICENSE) for details.
[node-ee]: https://nodejs.org/api/events.html#class-eventemitter