Simple Signals

A Typescript based simple signal framework.

For when all you need a simple way to trigger and listen for type safe events.

A longer description would be that signals are for handling events but each instance of a Signal is for representing a single event.

Install

To get from npm:

npm install --save simple-signals

Alternatively you can download the code and build it yourself with

npm run build

And in the dist folder will be the Javascript and Typescript typings file.

Also the whole thing is one Typescript file so it's pretty easy to manually add it to your own source code.

Features

• Small file size (about 0.3kb before compression)
• Type safe events
• Very simple API, only 3 methods.
• No dependencies

Example

Signals are a way to represent a single event with type safety.

import Signal from "simple-signals";
 
const newName = new Signal<string>();
const remove1 = newName.add((name) =>
{
    console.log('New name 1:', name);
});
const remove2 = newName.add((name) =>
{
    console.log('New name 2:', name);
});
 
console.log(newName.length()) // 2
newName.trigger('Foo');
// Console prints
// New name 1: Foo
// New name 2: Foo
 
remove1();
 
console.log(newName.length()) // 1
newName.trigger('Bar');
// Console prints
// New name 2: Bar

API

Types

// Listener for when a signal is dispatched.
// Can return false to stop the next signal from triggering.
export type SignalListener<T> = (value: T) => void | boolean;
 
// A function used to remove a listener from the signal.
export type RemoveListener = () => void;

Signal

The main class that keeps track of added signal listeners.

length

returns: number The number of active listeners.

add

listeners: SubscriptionListener<T> A function that will be called when the signal is triggered. The function can optionally return a boolean (false) to prevent further listeners from triggering.

returns: RemoveListener A function to remove the listener from the store.

Add a listener to the signal, returns a function for removing the listener.

The order of added listeners is maintained.

trigger

value: T The value to pass to each of the triggered listeners.

Triggers the listeners on the signal with the value given.

License

MIT

Author

Alan Lawrey 2020