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djipevents


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DjipEvents

DjipEvents is an event-handling library that can be used in the browser and in Node.js. It is small (under 3KB) but yet powerful. It features methods to register, trigger and delete events. It is a mostly abstract class meant to be extended by (or mixed into) other objects.

It is currently available in 3 flavours:

  • ESM: native ES6 module syntax for modern browsers
  • CommonJS: ES5 syntax for Node.js (and bundlers such as Webpack)
  • IIFE: ES5 syntax for legacy browser support (via <script> tag)

Importing into project

Native ES6 module syntax in browsers

This is for use in modern browsers that support the ECMAScript 6 syntax for module imports and exports. Going forward, this should be the preferred way to import the library (if your target environment supports it):

import {EventEmitter} from "./node_modules/djipevents/dist/esm/djipevents.esm.min.js";

Note that the library (purposely) does not provide a default export. This means you have to use curly quotes when importing.

Native ES6 module syntax in Node.js

Since Node.js v12 it is possible to use the "import" keyword to import external modules. In this case, you can use the following syntax:

import {EventEmitter} from "djipevents";

Note that, to use ES6 modules in Node.js, your package.json file must have the following property:

{
  "type": "module"
}

CommonJS format in Node.js

Obviously, you can also use the traditional CommonJS syntax traditionnaly used in the Node.js world.

Even though Node.js already offers its own EventEmitter object, you can still use djipevents if you prefer its added functionalities:

const {EventEmitter} = require("djipevents");

Object in global namespace (djipevents)

This is mostly for legacy-browser support and quick testing. It might be easier for some as it is a very common approach:

<script src="node_modules/djipevents/dist/iife/djipevents.iife.min.js"></script>

CDN-Hosted Versions

All three versions of the library (ES6 Module, CommonJS and IIFE) are available via a CDN. Here is the syntax for the global version:

<script src="https://cdn.jsdelivr.net/npm/djipevents@2.0.0/dist/iife/djipevents.iife.min.js"></script>

For the other versions, just change iife for esm (ES6 Module) or cjs (CommonJS) version.

Key features

This library is nothing extraordinary but it does have some interesting features not necessarily found in the browser's EventTarget, in Node.js' EventEmitter or even in other libraries:

  • Listeners can be set to expire with the duration option;
  • The Listener object returned by addListener() has a remove() method that allows you to easily remove the listener.
  • Listeners can be set to trigger an arbitrary number of times with the remaining option;
  • It is possible to listen to all events by using EventEmitter.ANY_EVENT.
  • The waitFor() method returns a promise that is fulfilled when an event occurs. A duration can also be defined so that the promise is automatically rejected if the event does not occur within the specified duration.
  • You can pass any number of arguments to the callback function by using the arguments option of addListener(). You can also prepend even more arguments by passing them to emit().
  • You can set the value of this in the callback by using the context option. This saves you from using JavaScript's relatively slow bind() method.
  • The callback function can be accessed via the callback property of the Listener object. This makes it especially easy to access bound versions of functions transformed by using the context option or by manually calling bind().
  • The emit() method returns an array containing the return value of all the callback functions;

Hidden goodies

As you can see in the reference, the API is lean. It is meant to be that way. That does not mean the library is less powerful than others. Some functionalities are just less glaringly obvious than with some other libraries. For example:

  • While djipevents does not have a removeAllEventListeners() method, you can achieve the same by calling removeListener() with no arguments.

  • There is no once() method, use addOneTimeListener().

  • There is no prependListener() method. Just use addListener() with the prepend option.

  • There are no on() and off() methods either. Just use addListener() and removeListener().

As far as I'm concerned, on(), off() and once() are very poor method names. Once you start extending or mixing in this library, you realize that identifiers such as on and off are collision-prone and do not describe properly what the methods are actually doing, which is bad. It is true that once()is shorter than addOneTimeListener(). However, with auto-completion, this is irrelevant.

API Reference

This library is quite straightforward and I did not take time to create usage examples. However, I did take some time to create a complete API Reference which should be enough for most to get started.

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Last updated on 13 Dec 2022

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