In this blog post, we will look into what are entryComponents, why is the purpose of entryComponents, why do we no longer need to use them after Angular Ivy.

With angular 9, there has been a lot of talking going on around entryComponents, and the Angular developers who had not been much aware of entryComponents have now been interested in knowing more about it.

In this blog post, I will try to cover everything that might help you clear up all the thoughts you have around the usage, importance, and the goodbye of 

The best way to start understanding what 

are would be by first trying to understand component renders in Angular and how really does the compiler play a role here.

So just for a visual understanding of what we are talking right now, I have added below a snapshot of the component declarations inside the root module.

Basically, there are two types of component declarations, ones which are included as a reference insides templates, and the other ones which are loaded imperatively.

What does this mean and what is the difference?

When we reference the component inside templates using the component selector, that’s the declarative way of writing components.

Now, the browser doesn’t really understand what 

 means, and therefore compiling it down to what browser would be able to understand is exactly the Angular compiler’s job.

The imperatively written template for, for example, 

const el = document.createElement('app-instruction-card');
const cmp = new AppInstructionCardCmp();

renderComponent(el, cmp);

if(ctx.val !== oldValue) {
  cmp.value = ctx.val;
  oldValue = cmp.value;
  ng.updateView(el, cmp);
}

This creates an element with your component name and registers it with the browser. It also checks for change detection by comparing the old Value with the current value and updates the view accordingly.

We write templates declaratively since the Angular compiler does this rendering bit for us.

Now, this is where we we can introduce ourselves to what entryComponents are!

Before Ivy, Angular would create Ngfactories for all the components declared in the template and as per the NgModule configuration. During the runtime it would enable tree shaking for the components not used. This is why the dynamic components with no Ngfactories could not be rendered and would throw an error like:

 array would then make the factories for these dynamic components available at runtime.

How Angular specifies a component as an entryComponent behind the hood can be in different ways.

Using ngDoBootstrap() and using the same imperative code to declare a component bootstraps it and makes it an entry component into the browser.

Now, you’d be wondering that if entryComponents have such a massive role to play in component declaration, why do we as developers see it rarely used? 

As we discussed above, entryComponents are mostly specified in two ways, bootstrapping them or defining them in a router definition. But since these happen under the hood, we hardly notice it. However, when working with dynamic components, or web components in Angular, we explicity define the components as entry Components inside the 

, we can define the component inside this array:

Role of entryComponents in smaller bundle sizes?

Alright, think for a minute. When we declare multiple components inside the declarations array of our modules, does that mean all these components will be included inside the final bundle?

 have a role to play. So the answer first of all to the above question is NO. All declared components aren’t necessarily present in the final produced bundle. It is if they are specified as entryComponents what decides if they’d be present in the produced bundle.

This basically means that all the routable components will be present in the bundle for sure and also the bootstrap component obviously. This would also include the bundles that are declared inside the templates of other components. However, the tree shaking process will get rid of all the unused components with no reference without having to include them inside the package.

 are mostly explicity defined when dealing with dynamic components, like I said before. This is because there needs to be a reference for the compiler to understand that 

, there is no reference for a particular component in the template or router for now, there is a possibility for it to be rendered dynamically when required. The 

takes care of creating this dynamic component for us but we specify this inside the entryComponents array inside NgModule.

If you have worked with dynamic components before, you might have faced an error like:

Coming to the point why entryComponents are no longer required.

Now knowing why need entryComponents, lets discuss a scenario where in we have created a dynamic component and have added it to the entryComponents array.

This basically means that now since we explicitly declared it as an entryComponent, the tree shaker would not prune this component thinking that it doesn’t have a reference in the template. Also, specifying it as an entryComponent would create a component factory for this dynamic component.

 for a particular dynamic component could be added automatically whenever a dynamic component was created to be used. So this would save the developer from specifying it everytime to make sure the compiler knows the component. One more issue with using entry component was referencing the entryComponents declared inside a lazily loaded module. So if a lazy loaded module contains a modal component as an entry component, you’d face an error like 

No component factory found for this component.

 This was because the root injector couldn’t be referenced to create a component factory for the entryComponent. One solution, though not very promising was creating a component resolver factory yourself for a particular entry component inside the lazy loaded module to be able to execute it.

With Angular 9 coming in and Ivy as the new rendering engine

, all the components would be considered as 

 and do not necessarily need to specified inside the entryComponents array.

With Ivy, the components will have locality and this means that dynamically importing these dynamic components will always work regardless of presence of 

This is because NOW, the presence of the @Component decorator would mean that the factories would be generated for this component and this happens due to the 

ngtsc compiler which is like a set of TypeScript transformers 

and these transformers introduce the static properties 

. These static properties are then able to easily access the code required for instantiating a component/module etc.

See the update from the Angular official documentation here:

https://next.angular.io/guide/deprecations#entrycomponents-and-analyz

A demo here shows how entryComponents are no longer required with Angular 9

https://ng-run.com/edit/c8U6CpMLbfGBDr86PUI0

Some more references to be curious about:

In this blog post, we talked about the need of 

array when dealing with dynamic components or web components 

for the components by specifying it in the entryComponents array and the presence of Component decorator provides the code required for the instantiation of the components ensuring that the compiler is aware of the presence of these 

AUTHOR

Nishu Goel

Bye bye, entryComponents?

Creating a Drag-n-Drop Email Editor with Angular

Building a good, reliable drag-n-drop email editor is hard. Every time we wanted to add one in any of our projects, there weren’t many good options available that were polished and reliable enough for commercial use.

After months of search, we decided to build one that can be embedded in any web app within 5 minutes. It’s available on 

It takes care of all the unsexy and boring stuff that comes with building a reliable and solid email editor / page builder. Things like outputting the correct HTML syntax, and making sure it looks and works fine in all old browsers and email clients (Hey, IE & Outlook =).

The easiest way to use Angular Email Editor is to install it from npm or Yarn and include it in your own Angular build process.

Next, you'll need to import the Email Editor module in the app module.

import { EmailEditorModule } from 'angular-email-editor';
...

@NgModule({
  ...
  imports: [ EmailEditorModule ],
  ...
});

import { Component, ViewChild } from '@angular/core';
import { EmailEditorComponent } from 'angular-email-editor';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  title = 'angular-email-editor';

  @ViewChild(EmailEditorComponent)
  private emailEditor: EmailEditorComponent;
}

That’s it. This should render a fully functional drag-n-drop editor in your Angular app.

Now that we have a fully functional email editor, we need to save the HTML it outputs. The editor exposes a method called 

We'll add a button that calls exportHtml.

import { Component, ViewChild } from '@angular/core';
import { EmailEditorComponent } from 'angular-email-editor';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  title = 'angular-email-editor';

  @ViewChild(EmailEditorComponent)
  private emailEditor: EmailEditorComponent;

  exportHtml() {
    this.emailEditor.exportHtml((data) => console.log('exportHtml', data));
  }
}

<div class="container">
  <button (click)="exportHtml()">Export</button>
  <email-editor></email-editor>
</div>

While HTML is the final result of the design, you will need to save the work done in the email editor for future use. There are a number of use cases for this such as:

Our email editor saves all work in JSON format. You can save the JSON and then pass it when loading the editor again and it will resume from where you left.

import { Component, ViewChild } from '@angular/core';
import { EmailEditorComponent } from 'angular-email-editor';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  title = 'angular-email-editor';

  @ViewChild(EmailEditorComponent)
  private emailEditor: EmailEditorComponent;

  saveDesign() {
    this.emailEditor.saveDesign((design) => console.log('saveDesign', design));
  }
}

<div class="container">
  <button (click)="saveDesign()">Save Design</button>
  <email-editor></email-editor>
</div>

Once you have the JSON saved, you can pass it to the editor using the 

import { Component, ViewChild } from '@angular/core';
import { EmailEditorComponent } from 'angular-email-editor';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  title = 'angular-email-editor';

  @ViewChild(EmailEditorComponent)
  private emailEditor: EmailEditorComponent;

  editorLoaded() {
    const json = /* DESIGN JSON GOES HERE */
    this.emailEditor.loadDesign(json);
  }
}

https://angular-email-editor-demo.netlify.com/

Learn

The newline Guide to Building Your First GraphQL Server with Node and TypeScript

Teach

Amelia Wattenberger

Author of Fullstack D3

Community

The Future Of Software engineering and AI: What YOU can do about it

Tutorials on Html Template

Bye bye, entryComponents?

Creating a Drag-n-Drop Email Editor with Angular

This has been a really good investment!

Advance your career with newline Pro.

Email Newsletter

Popular Topics

Masterclasses

Tutorials

Fullstack React with TypeScript