Preloading

Strategies for Angular Modules

Angular RTP Meetup

@AskUdhay

Hey, Am Udhay (OO-dhy)

Agenda

  • Single Module Angular App
  • Multi Module Angular App
  • Lazy loading
  • Preloading Modules:
    • All
    • Selective
    • Network based
    • Quick link
  • Discussion (Q/A)

 

@AskUdhay

Single Module Angular App

@AskUdhay

  • App contains only one module that has Components, Pipes, Directives and Services.
  • It works great for small web application with five to ten pages. 

Module

Components

Pipes

Directives

Multi Module Angular App

@AskUdhay

  • App contains more than one module with App module being the root module. Each modules contains Components, Pipes, Directives and Services.
  • It works great for Enterprise level applications

Root / Main

Home

Products

Cart

Payment

Orders

Lazy loading

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Lazy loading

  • Loads Angular Module only when the route is visited / accessed.

@AskUdhay

Root / Main

Home

Products

Cart

Payment

Orders

/home

/products

/cart

/billing

/orders

https://someonlinestore.com/

Lazy loading (Contd)

Create new Angular project

@AskUdhay

ng new someonlinestore --routing
ng generate module payment --route billing --module app.module

Create feature module (Angular takes care of lazy loading configuraiton)

Lazy loading (Contd)

Application's Root Module Routes look like:

@AskUdhay

const routes: Routes = [
  {
    path: 'billing',
    loadChildren: () => 
    	import('./payment/payment.module').
        		then((m) => m.PaymentModule),
  }
];

When User accesses https://someonlinestore.com/billing, Payment module gets loaded and their content painted on UI

Drawback of Lazy Loading

  • If the bundle (Feature module) size is huge, it makes User to wait couple moments to load the page when the respective route is accessed.

@AskUdhay

This can be fixed by Preloading the module that's huge in size based on different strategies. Let's dig into it more..

Preloading Strategy - All

Preload All Modules by setting preloadingStrategy router option as below:

@AskUdhay

@NgModule({
  imports: [
    RouterModule.forRoot(routes, 
        { preloadingStrategy: PreloadAllModules }
     ),
  ],
  exports: [RouterModule],
})

Preloading Strategy - Selective

Set Preload JSON parameter value to either true or false in the route. And update preloadingStrategy to SelectivePreloadStrategy (let's create it).

@AskUdhay

const routes: Routes = [  
  {
    path: 'home',
    loadChildren: () => import('./home/home.module').then((m) => m.HomeModule),
    data: {preload: true}
  },
  {
    path: 'about',
    loadChildren: () =>
      import('./about/about.module').then((m) => m.AboutModule),
    data: {preload: false} 
  }, 
];

@NgModule({
  imports: [
    RouterModule.forRoot(routes, {preloadingStrategy: SelectivePreloadStrategy}),
  ],
  exports: [RouterModule],
})

Preloading Strategy - Selective (Contd)

Create a Service class 'SelectivePreloadStrategy' & implement PreloadingStrategy Interface. Add logic within preload method that decides whether to preload module or not..

@AskUdhay

import { Injectable } from '@angular/core';
import { PreloadingStrategy, Route } from '@angular/router';
import { Observable, EMPTY } from 'rxjs';

@Injectable({
  providedIn: 'root'
})
export class SelectivePreloadStrategy implements PreloadingStrategy{

  constructor() { }

  preload(route: Route, load: () => Observable<any>): Observable<any>{
    return route.data && route.data['preload'] ? load() : EMPTY;
  }

}

@AskUdhay

const routes: Routes = [  
  {
    path: 'home',
    loadChildren: () => import('./home/home.module').then((m) => m.HomeModule),
    data: {preload: true}
  },
  {
    path: 'about',
    loadChildren: () =>
      import('./about/about.module').then((m) => m.AboutModule),
    data: {preload: false} 
  }, 
];

@NgModule({
  imports: [
    RouterModule.forRoot(routes, {preloadingStrategy: NetworkPreloadStrategy}),
  ],
  exports: [RouterModule],
})

Preloading Strategy - Network Connection Based

Update preloadingStrategy to NetworkPreloadStrategy (let's create it).

@AskUdhay

import { Injectable } from '@angular/core';
import { PreloadingStrategy } from '@angular/router';
import { EMPTY, TimeoutError } from 'rxjs';

export declare var navigator;

@Injectable({
  providedIn: 'root'
})
export class NetworkPreloadStrategy implements PreloadingStrategy{

  constructor() { }
  preload(route: import("@angular/router").Route, load: () => import("rxjs").Observable<any>): import("rxjs").Observable<any> {
    return this.hasGoodNetworkConn() ? load() : EMPTY;
  }

  hasGoodNetworkConn() {
    const conn = navigator.connection;
    if(conn){
      const connectionsToAvoid = ['2g', '3g'];
      const connectionType = conn.effectiveType || '';
      console.log(connectionType);
      if(connectionsToAvoid.includes(connectionType)){
          return false;
      }
    }   
    return true;
  }
}

Preloading Strategy - Network Connection Based (Contd)

Decide preloading based on Network..

Preloading Strategy - Quick Links Strategy

@AskUdhay

const routes: Routes = [  
  {
    path: 'home',
    loadChildren: () => import('./home/home.module').then((m) => m.HomeModule),
    data: {preload: true}
  },
  {
    path: 'about',
    loadChildren: () =>
      import('./about/about.module').then((m) => m.AboutModule),
    data: {preload: false} 
  }, 
];

@NgModule({
  imports: [
    RouterModule.forRoot(routes, {preloadingStrategy: QuickLinkStrategy}),
  ],
  exports: [RouterModule],
})

Using ngx-quicklink, the configuration is straightforward..

Import the QuicklinkModule in AppModule and add QuickLinkStrategy as Preloading strategy

Links

Code - https://github.com/askudhay/pokemon-app

App -  https://ngpokemon-62a15.web.app/

Twitter-  https://twitter.com/AskUdhay

Check my previous talks -  http://askudhay.com/

ng Thanks!

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