Atch (updated fork of 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

Atch 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.

$ npm install --save @victor141516/atch

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

// using ES6 modules
import atch from '@victor141516/atch';

// using CommonJS modules
var atch = require('@victor141516/atch');

Usage

import atch from '@victor141516/atch';

const emitter = atch();

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

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

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

// clearing all events
emitter.all.clear();

// working with handler references:
function onFoo() {}
emitter.on('foo', onFoo); // listen
emitter.off('foo', onFoo); // unlisten

Typescript

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

import atch from '@victor141516/atch';

type Events = {
  foo: string;
  bar?: number;
};

const emitter = atch<Events>(); // inferred as Emitter<Events>

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

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

Alternatively, you can use the provided Emitter type:

import atch, { Emitter } from '@victor141516/atch';

type Events = {
  foo: string;
  bar?: number;
};

const emitter: Emitter<Events> = atch<Events>();

Examples & Demos

API

Table of Contents

• atch
• all
• on
  • Parameters
• once
  • Parameters
• waitFor
  • Parameters
• off
  • Parameters
• emit
  • Parameters

atch

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

Returns Atch

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

Returns Function De-register function which will undo the event registration

once

Register an event handler for the given type that will only be called once.

Parameters

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

Returns Function De-register function which will undo the event registration

waitFor

Wait for the next event of type to be emitted.

Parameters

• type (string | symbol) Type of event to wait for

Returns Promise<Any> Promise that will resolve when the event is emitted

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 ('*' to remove a wildcard handler)
• 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/<your-username>/atch
• Navigate to the newly cloned directory: cd atch
• 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