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https://github.com/damianc/pubsub
Implementation of the PubSub pattern.
https://github.com/damianc/pubsub
Last synced: about 1 month ago
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Implementation of the PubSub pattern.
- Host: GitHub
- URL: https://github.com/damianc/pubsub
- Owner: damianc
- Created: 2023-12-16T08:29:18.000Z (about 1 year ago)
- Default Branch: master
- Last Pushed: 2023-12-16T09:34:32.000Z (about 1 year ago)
- Last Synced: 2023-12-17T09:54:02.811Z (about 1 year ago)
- Language: JavaScript
- Size: 4.88 KB
- Stars: 0
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
Awesome Lists containing this project
README
# PubSub
Implementation of the PubSub pattern.
```
const ps = PubSub();
ps.sub(val => console.log('value: ' + val));
ps.pub(1);
// value: 1
ps.pub(2);
// value: 2
```
## Overview
```
PubSub(
cachedItemsNumber = 0,
cachedInitItems = [],
pubCachedOnSub = false
)
```
**Parameters**
- `cachedItemsNumber: number` - a number of items to cache
- `cachedInitItems: any[]` - initial content of cache; if it's an array whose length exceeds the `cachedItemsNumber` value, only last elements are taken
- `pubCachedOnSub: boolean` - if `true`, newly added subscriber will be fired immediately with cached values
**Return value**
Returns object with following members:
- `subscribers: number` - a number of subscribers
- `isCached: boolean` - whether values are cached
- `cacheSize: number` - a number of items being cached
- `valuesEmitted: number` - a number of times any value was emitted
- `sub(subscriber: Function): Function` - adds a subscriber and returns it
- `unsub(subscriber: Function): Function` - removes the subscriber and returns it
- `unsubAll(): void` - removes all subscribers
- `pub(value: any): void` - emits a value to subscribers
`subscriber` is a function that takes two arguments - `(value, meta)`:
- `value` - emitted value
- `meta` - object with following members:
- `pubOnSubCall: boolean` - if `pubCachedOnSub` parameter of the `PubSub()` constructor was set to `true`, it states whether a current call of a subscriber is automatic and takes place due to addition of the subscriber
- `stop: Symbol` - return it from a subscriber to stop the flow of a value and prevent remaining subscribers from handling the value
## Examples
### Use of the `unsub()` method
```
const ps = PubSub();
const subA$ = ps.sub(val => console.log('A: ' + val));
const subB$ = ps.sub(val => console.log('B: ' + val));
ps.pub(1);
// A: 1
// B: 1
ps.unsub(subA$);
ps.pub(2);
// B: 2
```
### Use of the `stop` symbol
```
let i = 0;
const ps = PubSub();
ps.sub((val, meta) => {
i++;
console.log('A: ' + val);
if (i === 2) return meta.stop;
});
ps.sub(val => {
console.log('B: ' + val);
});
ps.pub(1);
// A: 1
// B: 1
ps.pub(2);
// A: 2
ps.pub(3);
// A: 3
// B: 3
```
### Cache
```
const ps = PubSub(2, [10,20], true);
ps.sub(val => console.log('A: ' + val));
// A: 10,20
ps.pub(1);
// A: 20,1
ps.sub(val => console.log('B: ' + val));
// B: 20,1
ps.pub(2);
// A: 1,2
// B: 1,2
/*
exceptionally, do not emit cached items
on sub in this subscriber
*/
ps.sub((val, meta) => {
if (!meta.pubOnSubCall) {
console.log('C: ' + val);
}
});
ps.pub(3);
// A: 2,3
// B: 2,3
// C: 2,3
```