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Learn about Hydration in Angular

Hydration in Angular

In Angular, hydration refers to the process of converting server-side rendered HTML into a fully interactive Angular application on the client-side. This process involves initializing Angular components, binding data, setting up event listeners, and enabling Angular's change detection mechanism.

When a user navigates to an Angular application, the initial HTML content is usually generated on the server and sent to the client. This static HTML is then "hydrated" by Angular, meaning that Angular takes control of the DOM (Document Object Model) and turns it into a dynamic and interactive application.

During hydration, Angular bootstraps the application, instantiates the root module, and starts the dependency injection process. It also sets up the router and initializes any services or components that are necessary for the initial rendering of the page. Once the hydration process is complete, the Angular application is fully functional, and users can interact with it seamlessly.

Hydration is crucial for Angular Universal applications, which are designed to run both on the client and the server. In such applications, the initial rendering occurs on the server, and then Angular hydrates the static HTML on the client-side to provide interactivity and responsiveness. This approach improves performance and SEO (Search Engine Optimization) by providing a fully rendered page to web crawlers and users who have disabled JavaScript.

Let's walk through the steps involved in the hydration process with some sample code:

Bootstrap the Angular Application

In the main.ts file, the Angular application is bootstrapped by calling the platformBrowserDynamic().bootstrapModule() function. This function loads the root module of the application and starts the Angular application.

import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';
import { AppModule } from './app/app.module';

platformBrowserDynamic().bootstrapModule(AppModule)
  .catch(err => console.error(err));

Root Module Initialization

In the AppModule (or whatever your root module is named), Angular initializes various components, services, and other application features.

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { AppComponent } from './app.component';

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }

Component Rendering

Once the root module is initialized, Angular starts rendering the application's components. This typically starts with the root component, such as AppComponent.

import { Component } from '@angular/core';

@Component({
  selector: 'app-root',
  template: `
    <h1>Welcome to My Angular App</h1>
    <!-- Other components and directives can be included here -->
  `
})
export class AppComponent {
  // Component logic can go here
}

Change Detection and Event Handling

Angular sets up change detection to monitor for changes to the application's state. This allows Angular to update the DOM when data changes and respond to user interactions.

import { Component } from '@angular/core';

@Component({
  selector: 'app-root',
  template: `
    <h1>Welcome to My Angular App</h1>
    <button (click)="onClick()">Click me</button>
  `
})
export class AppComponent {
  onClick(): void {
    console.log('Button clicked!');
  }
}

import { Component } from '@angular/core';

@Component({
  selector: 'app-root',
  template: `
    <h1>Welcome to My Angular App</h1>
    <button (click)="onClick()">Click me</button>
  `
})
export class AppComponent {
  onClick(): void {
    console.log('Button clicked!');
  }
}

Complete Hydration

Once all components are rendered, services are initialized, and event listeners are set up, the hydration process is complete. The Angular application is now fully functional and interactive.

This code demonstrates the basic steps involved in the hydration process of an Angular application. During hydration, Angular converts static HTML into a dynamic and interactive application on the client-side, enabling users to interact with the application seamlessly.


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