Mitt

Tiny 200 byte functional event emitter / pubsub.

PubSub
developit/mittmitt

README

mitt
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Mitt


Tiny 200b functional event emitter / pubsub.


-   Microscopic: weighs less than 200 bytes gzipped
-   Useful: a wildcard "*" event type listens to all events
-   Familiar: same names & ideas as Node's EventEmitter
-   Functional: methods don't rely on this
-   Great Name: somehow mitt wasn't taken

Mitt was made for the browser, but works in any JavaScript runtime. It has no dependencies and supports IE9+.

Table of Contents


-   Install
-   Usage
-   Examples & Demos
-   API
-   Contribute
-   License

Install


This project uses node and npm. Go check them out if you don't have them locally installed.

  1. ```sh
  2. $ npm install --save mitt
  3. ```

Then with a module bundler like rollup or webpack, use as you would anything else:

  1. ``` js
  2. // using ES6 modules
  3. import mitt from 'mitt'

  5. // using CommonJS modules
  6. var mitt = require('mitt')
  7. ```

The UMD build is also available on unpkg:

  1. ``` html
  2. <script src="https://unpkg.com/mitt/dist/mitt.umd.js"></script>
  3. ```

You can find the library on window.mitt.

Usage


  1. ``` js
  2. import mitt from 'mitt'

  4. const emitter = mitt()

  6. // listen to an event
  7. emitter.on('foo', e => console.log('foo', e) )

  9. // listen to all events
  10. emitter.on('*', (type, e) => console.log(type, e) )

  12. // fire an event
  13. emitter.emit('foo', { a: 'b' })

  15. // clearing all events
  16. emitter.all.clear()

  18. // working with handler references:
  19. function onFoo() {}
  20. emitter.on('foo', onFoo)   // listen
  21. emitter.off('foo', onFoo)  // unlisten
  22. ```

Typescript


Set "strict": true in your tsconfig.json to get improved type inference for mitt instance methods.

  1. ```ts
  2. import mitt from 'mitt';

  4. type Events = {
  5.   foo: string;
  6.   bar?: number;
  7. };

  9. const emitter = mitt<Events>(); // inferred as Emitter

  11. emitter.on('foo', (e) => {}); // 'e' has inferred type 'string'

  13. emitter.emit('foo', 42); // Error: Argument of type 'number' is not assignable to parameter of type 'string'. (2345)
  14. ```

Alternatively, you can use the provided Emitter type:

  1. ```ts
  2. import mitt, { Emitter } from 'mitt';

  4. type Events = {
  5.   foo: string;
  6.   bar?: number;
  7. };

  9. const emitter: Emitter<Events> = mitt<Events>();
  10. ```

Examples & Demos


Preact + Mitt Codepen Demo
preact + mitt preview


API




Table of Contents


-   mitt
-   all
-   on
    -   Parameters
-   off
    -   Parameters
-   emit
    -   Parameters

mitt


Mitt: Tiny (~200b) functional event emitter / pubsub.

Returns Mitt

all


A Map of event names to registered handler functions.

on


Register an event handler for the given type.

Parameters


-   type (string \| symbol) Type of event to listen for, or '*' for all events
-   handler Function Function to call in response to given event

off


Remove an event handler for the given type.
If handler is omitted, all handlers of the given type are removed.

Parameters


-   type (string \| symbol) Type of event to unregister handler from, or '*'
-   handler Function? Handler function to remove

emit


Invoke all handlers for the given type.
If present, '*' handlers are invoked after type-matched handlers.

Note: Manually firing '\*' handlers is not supported.

Parameters


-   type (string \| symbol) The event type to invoke
-   evt Any? Any value (object is recommended and powerful), passed to each handler

Contribute


First off, thanks for taking the time to contribute!
Now, take a moment to be sure your contributions make sense to everyone else.

Reporting Issues


Found a problem? Want a new feature? First of all see if your issue or idea has already been reported.
If don't, just open a new clear and descriptive issue.

Submitting pull requests


Pull requests are the greatest contributions, so be sure they are focused in scope, and do avoid unrelated commits.

-   Fork it!
- Clone your fork: `git clone https://github.com//mitt`
-   Navigate to the newly cloned directory: cd mitt
-   Create a new branch for the new feature: git checkout -b my-new-feature
-   Install the tools necessary for development: npm install
-   Make your changes.
-   Commit your changes: git commit -am 'Add some feature'
-   Push to the branch: git push origin my-new-feature
-   Submit a pull request with full remarks documenting your changes.

License


MIT License © Jason Miller