LoaderQueue

A simple Javascript queue manager for managing dynamic loading events

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[TOC]

Installation

> npm install loader-queue --save

The node package contains typings for TypeScript implementations

Purpose

The problem

Many dynamic loading managers involve HTTP interceptors, language specific modules, or framework specific implementations.

The following example might work well for simple processes, but does not offer great scalability options.

getDataLoading = false;
getMoreDataLoading = false

async GetData() {
  this.getDataLoading = true;
  // ...
  this.getDataLoading = false;
}

async GetMoreData(){
  this.getMoreDataLoading = true;
  // ...
  this.getMoreDataLoading = false;
}

OnInit(){
  this.GetData();
  this.GetMoreData();
}

<app-loader [hidden]="!getDataLoading && !getMoreDataLoading"></app-loader>

The LoadingQueue solution

To solve the problem of handling scalable and dynamic loading events, we introduce the LoaderQueue object.

The LoaderQueue serves as a queue manager that you can add and remove events from as needed. The idea being that as long as there is an event on the queue, that the application is still loading data.

Usage

import { LoaderQueue } from 'loader-queue';
// ... 
loaderQueue = new LoaderQueue();

async GetData() {

  // Adds the 'GetData' event to the LoaderQueue
  // returns the LoaderQueueEvent that was added
  const loader = await this.loaderQueue.add('GetData');
  
  // ... do stuff
  
  // Removes the LoaderQueueEvent from the queue
  loader.remove();
}

<!-- Loader will be hidden if the loaderQueue does not contain any events -->
<app-loader [hidden]="!loaderQueue.length"></app-loader>

Examples

Queue management

There are multiple ways to add and remove events to and from the LoaderQueue.

Event Names

The simplest way to manage the loading queue is to name the event with a string.

import { LoaderQueue } from 'loader-queue';

loaderQueue = new LoaderQueue();

async GetData() {
  // Create and add the LoaderQueueEvent
  const loader = await this.loaderQueue.add('GetData');

  // Method 1 - removes the exact instance added locally
  loader.remove();

  // Method 2 - removes all instances of 'GetData'
  this.loaderQueue.remove('GetData');

  // Method 3 - removes the first instance of 'GetData'
  this.loaderQueue.remove('GetData', false);
}

Promises

The LoaderQueue can also promises as event arguments and automatically remove the event from the queue once the promise has resolved

import { LoaderQueue } from 'loader-queue';

loaderQueue = new LoaderQueue();

initialize() {
  // All three promises will be added to the queue and removed automatically when each Promise resolves
  this.loaderQueue.add(this.GetData());
  this.loaderQueue.add(this.GetProducts());
  this.loaderQueue.add(this.GetCategories());
}

Events

Utilize the LoadingQueue.events to subscribe to and act upon queue changes. Be sure to unsubscribe from the events on component destruction.

import { LoaderQueue, QueueEventType } from 'loader-queue';

loaderQueue = new LoaderQueue();

this.loaderQueue.events.subscribe(
  (ev) => {
    switch (ev.type) {
      case QueueEventType.Add:
        console.log('Event added to queue');
        break;
      case QueueEventType.Remove:
        console.log('Event removed from queue');
        break;
      case QueueEventType.Clear:
        console.log('LoadingQueue cleared');
        break;
    }
  });

API

LoadingQueue

The main object that manages the loading queue.

LoadingQueue Methods

.add(event)

returns Promise<LoadingQueueEvent>

Adds an event to the LoadingQueue and automatically removes the event when the event resolves

Argument Name	Type	Description
event	Promise	Adds an event to the LoadingQueue and automatically removes the event when the event resolves

.add(event)

returns Promise<LoadingQueueEvent>

Adds an event to the LoadingQueue according to the string event name provided.

Argument Name	Type	Description
event	string	The name of the event to add to the LoadingQueue (Concatenates a unique identifier under the hood)

.remove(event)

returns Promise<void>

Removes the provided LoaderQueueEvent

Argument Name	Type	Description
event	LoaderQueueEvent	The event to remove

.remove(event, removeAll)

returns Promise<void>

Removes an event from the loading queue according to the string name provided.

Argument Name	Type	Description
event	string	Event string to remove from the current loader stack
removeAll?	boolean	Optional parameter to remove all instances or a single instance of the event string. (Default true)

.clear()

returns Promise<void>

Clears the current queue of all LoaderQueueEvents

LoadingQueue Parameters

.length

type number

The current length of the LoaderQueue.

.events

type Subject

RxJs Subject that can be subscribed to and emits all add, remove, and clear events of the LoadingQueue.

LoadingQueueEvent

The event object that the LoadingQueue stores and manipulates

LoadingQueueEvent Methods

.remove()

returns Promise<void>

Removes this event from the LoadingQueue.

LoadingQueueEvent Parameters

.common_id

type string

The string identifier corresponding to the event name passed into the LoadingQueue.add() method

.unique_id

type string

The unique identifier generated for the event

Utilities

HasLoaderQueue

type interface

Utility interface to specify a component to contain a LoaderQueue

Example:

import { HasLoaderQueue, LoaderQueue } from 'loader-queue';

export class MyComponent implements HasLoaderQueue { 
  constructor() { }

  loaderQueue = new LoaderQueue(); // Required by the HasLoaderQueue interface
}