What you always wanted to know about Angular Dependency Injection tree

If you didn’t dive deep into angular dependency injection mechanism, your mental model should be that in angular application we have some root injector with all merged providers, every component has its own injector and lazy loaded module introduces new injector.

But maybe there is some more you should be aware of?

Also a while ago, so-called Tree-Shakeable Tokens feature was merged into master branch. If you are like me, you probably want to know what has changed.

So it’s time to examine all these things and maybe find something new…

The Injector Tree#

Most of angular developers know that angular creates root injector with singleton providers. But seems there is another injector which is higher that injector.

As a developer I want to understand how angular builds injector tree. Here is how I see the top part of Angular injector tree:

Top part of Angular Injector Tree

This is not the entire tree. For now, there aren’t any components here. We’ll continue drawing later. But now let’s start with AppModule Injector since it’s most used part of angular.

Root AppModule Injector#

Well known angular application root injector is presented as AppModule Injectorin the picture above. As it has already been said, this injector collects all providers from transitive modules. It means that:

If we have a module with some providers and import this module directly in AppModule or in any other module, which has already been imported in AppModule, then those providers become application-wide providers.

According to this rule, MyService2 from EagerModule2 will be included into the root injector.

ComponentFactoryResolver is also added to the root module injector by Angular. This resolver is responsible for dynamic creation components since it stores factories of entryComponents.

It is also worth noting that among all other providers we can see Module Tokenswhich are actually types of all merged NgModules. We will come back to this later when will be exploring tree-shakeable tokens.

In order to initialize NgModule injector Angular uses AppModule factory, which is located in so-called module.ngfactory.js file.

AppModule factory

We can see that the factory returns the module definition with all merged providers. It should be well known by many developers.

Tip: If you have angular application in dev mode and want to see all providers from root AppModule injector then just open devtools console and write:

ng.probe(getAllAngularRootElements()[0]).injector.view.root.ngModule._providers
<>

There are also a lot of well known facts which I won’t describe here because they are well covered in angular documentation:

• https://angular.io/guide/ngmodule-faq
• https://angular.io/guide/hierarchical-dependency-injection

#angular #javascript #dependency-injection

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What you always wanted to know about Angular Dependency Injection tree

If you didn’t dive deep into angular dependency injection mechanism, your mental model should be that in angular application we have some root injector with all merged providers, every component has its own injector and lazy loaded module introduces new injector.

But maybe there is some more you should be aware of?

Also a while ago, so-called Tree-Shakeable Tokens feature was merged into master branch. If you are like me, you probably want to know what has changed.

So it’s time to examine all these things and maybe find something new…

The Injector Tree#

Most of angular developers know that angular creates root injector with singleton providers. But seems there is another injector which is higher that injector.

As a developer I want to understand how angular builds injector tree. Here is how I see the top part of Angular injector tree:

Top part of Angular Injector Tree

This is not the entire tree. For now, there aren’t any components here. We’ll continue drawing later. But now let’s start with AppModule Injector since it’s most used part of angular.

Root AppModule Injector#

Well known angular application root injector is presented as AppModule Injectorin the picture above. As it has already been said, this injector collects all providers from transitive modules. It means that:

If we have a module with some providers and import this module directly in AppModule or in any other module, which has already been imported in AppModule, then those providers become application-wide providers.

According to this rule, MyService2 from EagerModule2 will be included into the root injector.

ComponentFactoryResolver is also added to the root module injector by Angular. This resolver is responsible for dynamic creation components since it stores factories of entryComponents.

It is also worth noting that among all other providers we can see Module Tokenswhich are actually types of all merged NgModules. We will come back to this later when will be exploring tree-shakeable tokens.

In order to initialize NgModule injector Angular uses AppModule factory, which is located in so-called module.ngfactory.js file.

AppModule factory

We can see that the factory returns the module definition with all merged providers. It should be well known by many developers.

Tip: If you have angular application in dev mode and want to see all providers from root AppModule injector then just open devtools console and write:

ng.probe(getAllAngularRootElements()[0]).injector.view.root.ngModule._providers
<>

There are also a lot of well known facts which I won’t describe here because they are well covered in angular documentation:

• https://angular.io/guide/ngmodule-faq
• https://angular.io/guide/hierarchical-dependency-injection

#angular #javascript #dependency-injection

Install Angular - Angular Environment Setup Process

Angular is a TypeScript based framework that works in synchronization with HTML, CSS, and JavaScript. To work with angular, domain knowledge of these 3 is required.

1. Installing Node.js and npm
2. Installing Angular CLI
3. Creating workspace
4. Deploying your First App

In this article, you will get to know about the Angular Environment setup process. After reading this article, you will be able to install, setup, create, and launch your own application in Angular. So let’s start!!!

Install Angular in Easy Steps

For Installing Angular on your Machine, there are 2 prerequisites:

• Node.js
• npm Package Manager

Node.js

First you need to have Node.js installed as Angular require current, active LTS or maintenance LTS version of Node.js

Download and Install Node.js version suitable for your machine’s operating system.

Npm Package Manager

Angular, Angular CLI and Angular applications are dependent on npm packages. By installing Node.js, you have automatically installed the npm Package manager which will be the base for installing angular in your system. To check the presence of npm client and Angular version check of npm client, run this command:

1. npm -v

Installing Angular CLI

• Open Terminal/Command Prompt
• To install Angular CLI, run the below command:

1. npm install -g @angular/cli

· After executing the command, Angular CLI will get installed within some time. You can check it using the following command

1. ng --version

Workspace Creation

Now as your Angular CLI is installed, you need to create a workspace to work upon your application. Methods for it are:

• Using CLI
• Using Visual Studio Code

1. Using CLI

To create a workspace:

• Navigate to the desired directory where you want to create your workspace using cd command in the Terminal/Command prompt
• Then in the directory write this command on your terminal and provide the name of the app which you want to create. In my case I have mentioned DataFlair:

1. Ng new YourAppName

• After running this command, it will prompt you to select from various options about the CSS and other functionalities.

• To leave everything to default, simply press the Enter or the Return key.

#angular tutorials #angular cli install #angular environment setup #angular version check #download angular #install angular #install angular cli

Angular 9 Dependency Injection Example Tutorial

Dependencies are services or objects that a class needs to perform its function. DI is a coding pattern in which a class asks for dependencies from external sources rather than creating them itself.

In Angular, the DI framework provides declared dependencies to a class when that class is instantiated. This guide explains how DI works in Angular, and how you use it to make your apps flexible, efficient, and robust, as well as testable and maintainable.

Angular Dependency injection is an essential application design pattern. Angular has its dependency injection framework, and you really can’t build an Angular application without it. It’s used so widely that almost everyone just calls it DI.

#angular #angular 9 #angular dependency injection

Tree-shakable dependencies in Angular projects

Tree-shakable dependencies are easier to reason about and compile to smaller bundles.

#angular #dependency-injection #tree-shakable #testing #providers

Basics of Angular: Part-1

What is Angular? What it does? How we implement it in a project? So, here are some basics of angular to let you learn more about angular.

Angular is a Typescript-based open-source front-end web application platform. The Angular Team at Google and a community of individuals and corporations lead it. Angular lets you extend HTML’s syntax to express your apps’ components clearly. The angular resolves challenges while developing a single page and cross-platform applications. So, here the meaning of the single-page applications in angular is that the index.html file serves the app. And, the index.html file links other files to it.

We build angular applications with basic concepts which are NgModules. It provides a compilation context for components. At the beginning of an angular project, the command-line interface provides a built-in component which is the root component. But, NgModule can add a number of additional components. These can be created through a template or loaded from a router. This is what a compilation context about.

What is a Component in Angular?

Components are key features in Angular. It controls a patch of the screen called a view. A couple of components that we create on our own helps to build a whole application. In the end, the root component or the app component holds our entire application. The component has its business logic that it does to support the view inside the class. The class interacts with the view through an API of properties and methods. All the components added by us in the application are not linked to the index.html. But, they link to the app.component.html through the selectors. A component can be a component and not only a typescript class by adding a decorator @Component. Then, for further access, a class can import it. The decorator contains some metadata like selector, template, and style. Here’s an example of how a component decorator looks like:

@Component({
    selector: 'app-root',
    templateUrl: 'app.component.html',
    styleUrls: ['app.component.scss']
})

Role of App Module

Modules are the package of functionalities of our app. It gives Angular the information about which features does my app has and what feature it uses. It is an empty Typescript class, but we transform it by adding a decorator @NgModule. So, we have four properties that we set up on the object pass to @NgModule. The four properties are declarations, imports, providers, and bootstrap. All the built-in new components add up to the declarations array in @NgModule.

@NgModule({
declarations: [
  AppComponent,
],
imports: [
  BrowserModule,
  HttpClientModule,
  AppRoutingModule,
  FormsModule
],
bootstrap: [AppComponent]
})

What is Data Binding?

Data Binding is the communication between the Typescript code of the component and the template. So, we have different kinds of data binding given below:

• When there is a requirement to output data from our Typescript code in the HTML template. String interpolation handles this purpose like {{data}} in HTML file. Property Binding is also used for this purpose like [property] = “data”.
• When we want to trigger any event like clicking a button. Event Binding works while we react to user events like (event) = “expression”.
• When we can react to user events and output something at the same time. Two-way Binding is used like [(ngModel)] = “data”.

#angular #javascript #tech blogs #user interface (ui) #angular #angular fundamentals #angular tutorial #basics of angular