Pedlar

A utility for logically grouping the performance and destruction of side effects. Inspired by React's useEffect hook.

Problem

Most JavaScript frameworks have some type of "init" and "destroy" life cycle functions. For example, React has componentDidMount() and componentWillUnmount(); and similarly Angular has ngOnInit() and ngOnDestroy().

The problem with these functions is that often times the work that you have to do on "init" closely mirrors the work that you have to do on "destroy". So you end up with this highly coupled code split between two different functions.

Pedlar addresses that problem by letting you declare both the "init" and "destroy" logic at the same time in the same place. It's just not all run at the same time. The function that you pass to perform() (the side effect) is run immediately, and the function that you return from the side effect is not run until you tell Pedlar to destroy that side effect.

Additionally, there's also usually an "update" life cycle function (componentDidUpdate() / ngOnChanges()). Oftentimes identical or similar work takes place in the "update" and "init" functions. Pedlar also provides the ability to re-perform a particular effect at any time. It can even skip running the effect if dependencies that you specify have not changed!

Installation

# Install with yarn 
yarn add pedlar
 
# Or install with npm 
npm i pedlar

Examples

Simple Usage

import Pedlar from 'pedlar'
 
let pedlar = new Pedlar()
 
pedlar.perform(() => {
  console.log('Side effect 1 performed')
  return () => console.log('Side effect 1 cleaned up!')
})
 
// LOG: 'Side effect 1 performed'
 
pedlar.perform(() => {
  console.log('Side effect 2 performed')
  return () => console.log('Side effect 2 cleaned up!')
})
 
// LOG: 'Side effect 2 performed'
 
pedlar.destroyAll()
 
// LOG: 'Side effect 1 cleaned up!'
// LOG: 'Side effect 2 cleaned up!'

Add and automatically remove an event

import Pedlar from 'pedlar'
 
let pedlar = new Pedlar()
let el = document.getElementById('my-button')
 
// Adds the click event
pedlar.addEvent(el, 'click', () => console.log('My button was clicked'))
 
// ...
 
// Removes the click event, along with cleaning up all other side effects
pedlar.destroyAll()

Re-perform an event when dependencies have changed

import {Pedlar, PedlarEffect} from 'pedlar'
 
let pedlar = new Pedlar()
let consoleEffect: PedlarEffect
 
consoleEffect = pedlar.perform(() => {
  console.log('Side effect performed')
  return () => console.log('Side effect cleaned up!')
}, ['my-dependency'])
 
// LOG: 'Side effect performed'
// You can avoid this initial run of the side effect by
// calling `pedlar.create()` instead of `pedlar.perform()`
 
consoleEffect.perform(['my-dependency'])
// Effect is not performed again, dependencies have not changed
 
consoleEffect.perform(['my-changed-dependency'])
 
// LOG: 'Side effect cleaned up!'
// LOG: 'Side effect performed'

Types

PedlarEffect

A Pedlar Effect is the object returned from either Pedlar.perform() or Pedlar.create(). It has two properties:

• id - string - The ID of this effect. This ID can be passed to Pedlar.destroy() to individually destroy this effect.
• perform - (currentDependencies?) => void - Run the side effect. If dependencies are passed, the side effect will only be run if the dependencies have changed. If this is not the first time the side effect is being run, the destroyer (if one exists) will be executed before the side effect is re-run.

PedlarSideEffect

The side effect that you wish to run. This is a function that either returns nothing, or another function that cleans up the side effect.

API

create(sideEffect: PedlarSideEffect): PedlarEffect

Create a PedlarEffect without initially running the side effect. You can optionally return a function from the sideEffect that cleans it up. The side effect can be run at any time by invoking PedlarEffect.perform().

perform(sideEffect: PedlarSideEffect, dependencies?: any[]): PedlarEffect

Perform a side effect. You can optionally return a function from the sideEffect that cleans it up. The side effect can be re-run at any time by invoking PedlarEffect.perform().

This is very similar to the Pedlar.create() function, except that this also runs the side effect immediately.

destroy(id)

Clean up a particular side effect that has been performed.

import Pedlar from 'pedlar'
 
let pedlar = new Pedlar()
 
let {id} = pedlar.perform(() => {
  console.log('Side effect 1 performed')
  return () => console.log('Side effect 1 cleaned up!')
})
 
pedlar.destroy(id)

destroyAll()

Clean up all side effects that have been performed since the last time this function was called.

addEvent(el, eventType, handler, options)

Perform the specific side effect of adding an event listener to an element. This event is then automatically removed when the side effect is destroyed.

Argument name	Type	Description
element	Element	The element to add the event listener to
eventType	keyof HTMLElementEventMap (string)	The type of event to add
handler	EventListenerOrEventListenerObject	The event handler
options	boolean \| EventListenerOptions	Optional. These options get passed directly through to the addEventListener function.

addCustomEvent(el, eventType, handler, options)

Identical to addEvent() except that the eventType argument accepts any string