[Tutorial]: Ionic Tutorials (Lazy Loading and How it affects performance)

in #utopian-io5 years ago

image source

Repository: Ionic Github Repository

Software Requirements:
Visual Studio Code(Or any preferred code editor)

What you will learn:
In this tutorial you would learn about lazy loading using the browser module coveering these major concepts

  • Learn how to use the browser module in ionic.
  • Learn how to boost performance using lazy loading
  • Learning how to migrate to lazy loading.

Difficulty: Intermediate

In this tutorial we would be dealing with a very critical aspect of any ionic developers development process which is lazy loading. For large apps with a lot of pages, without lazy loading it is almost certain that there would be a start-up lag.

First What is Lazy Loading?
Lazy loading in ionic was adopted from angular's lazy loading which was used to load images as they are needed so as to reduce the processing intensity of the device.
Lazy loading simply means creating pages or any components whenever they are needed and destroying them when they aren't needed. For a big app of about 10 or 20 pages, trying to load all at start-up would most certainly cause a lag and so it is better to load only the pages that would be used on startup. This would mean that you would load your login(if you have one) and maybe you tabs. This would go a long way in increasing the performance of your application.

So lets get coding

We'll start up with a project with a page that isn't lazy loaded and i'll walk you through lazy loading this page. Note however that in ionic 4, Lazy loading is quite different and more innate to the update. You could see a single paged minimized code for this tutorial on my github page at the end of the tutorial.

Well start with a home page generated with a tabs starter template.
To do that i would assume you already have ionic installed so simply head to you terminal and type

ionic start LazyLoading tabs//Note that 'LazyLoading is the name of the project and doesnt affect the way the project is generated

So you should have a started template
Head to your terminal and type

ionic g page newPage//This would generate a new page called 'newPage'

The thing about ionic 3 is that it automatically generates pages lazily loaded when you generate them with the terminal
Lets look at this newly generated lazy loaded page and what makes it lazy loaded.
Navigate to this directory


They would be four files inside the directory

Screenshot (68).png

The difference between is in the fourth file which is newPage.module.ts
This is the file that gives the page its independence. Pages that aren't lazy loaded are input directly to the app.module.ts. But when pages are lazy loaded, they have their own module which generates them immediately when needed.

Lets look into the structure of this file

import { NgModule } from '@angular/core';
import { IonicPageModule } from 'ionic-angular';
import { NewPage } from './new';

  declarations: [
  imports: [
export class NewPageModule {}![Screenshot (68).png](https://cdn.steemitimages.com/DQmaNsygSi9m9MK2xdjtCX6TeMjbj5gbb6rp5yBEkz8kXsD/Screenshot%20(68).png)

We see that the page exports an instance of itself to the app through this module.
Also you have to take note that in a lazy loaded page the newPage.ts file is decorated with the @IonicPage. Which can be imported from ionic-angular. Without this the page would not be read as a lazy loaded page.

The next thing you would need to know about lazy loading takes us to our app module
Note: This step would be very useful if you would want to migrate a fully normal app to a lazy loaded app. In newer releases of ionic 3(meaning that you generated the page more recently this wouldnt be needed). But you should check however.

Head to the directory below


This is how it should look

import { NgModule, ErrorHandler } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';//This is the module related with lazy loading
import { IonicApp, IonicModule, IonicErrorHandler } from 'ionic-angular';
import { MyApp } from './app.component';

import { AboutPage } from '../pages/about/about';
import { ContactPage } from '../pages/contact/contact';
import { HomePage } from '../pages/home/home';
import { TabsPage } from '../pages/tabs/tabs';

import { StatusBar } from '@ionic-native/status-bar';
import { SplashScreen } from '@ionic-native/splash-screen';

  declarations: [
  imports: [
  bootstrap: [IonicApp],
  entryComponents: [
  providers: [
    {provide: ErrorHandler, useClass: IonicErrorHandler}
export class AppModule {}

As you can see in the comment in the above code. You would take note of the BrowserModule which is an angular style module that navigates to pages similarly to the way a browser would navigate to pages based on url's

**Navigating to a lazy loaded pageAs per ionic, navigation is carried out by thenavCtrl`` which is by default in the contructor of every generated page. Just as stated above the navigation for lazy loaded pages is more angular style. Which uses url paths.

To navigate to this newPage from the any other page we would need to state the page as a string
For instance to navigate to our new Lazy loaded page we would simply use this line of code


The beauty of this is that there is no need for any imports into any page or any module. The Browser module fixes this for us.
Screenshot (69).png
As seen above this uses the url path and adds that page to the stack . Simple and Easy.

You can find the minified code for this in my GIthub

Leave any comments below


Thank you for the contribution.
So few points:

  • You refer in your code to newPage (for example newPage.module.ts), although your screenshot shows no newPage and uses instead new.module.ts and relevant variations. Your directory structure is also slightly different. Is this screenshot not yours? or how did this happen?
  • Your text formatting has some serious issues. With so many contributions on the tutorial category, I do not understand why you still face such issues.
  • Why did you include a minified version of your code instead of a standard version? and how do you define that this is minified?
  • Your code file has no extension, how come? and also you added a text string at the end, so your code cannot function out of the box:

this is how to push a new page to the stack
this.navCtrl.push('NewPage')//Must be a string

  • In the tutorial, you point users to go to a directory, while that is not even a directory.

Head to the directory below

  • I do not believe you included enough details in the tutorial, and with all the confusing aspects highlighted above, it would be essential to see improvements over all those points.

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Thanks for the points

  • I would be grateful if you could expatiate on the areas where I got the text formatting wrong so I could improve on the next
  • Secondly, the code in my repo was sort of minimized so I could get all the code for the tutorial into a single file. In tutorials dealing with a single concept uploading the whole project would make it hard to find the exact files were dealing with. So I specify the file path in the tutorial and put them together in the GITHUB repo. All files are typescript files.
  • And lastly the file path stated in the last point would be easily found if the tutorial processes are being followed. The starter template includes all the folders when you run the starter command as stated at the beginning of the tutorial.
    Thanks for the review

Some examples...

Basically no real headers or proper separators.

About the github repo, no you do not need to put everything in a single file. Upload your project work, and pinpoint the files you are using, just like you did in the tutorial, but use correct file names. I still do not understand the difference in file names and structure compared to your screenshot, which is point three. Having such a difference is terribly confusing for the reader, and shows low tutorial quality content.

Thanks a lot
I'd certainly use these points when writing the next

Thank you for your review, @mcfarhat! Keep up the good work!

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