Directive that improves image loading performance by enforcing best practices.

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Selectors

• img[ngSrc]

Properties

<img ngSrc="hello.jpg" ngSrcset="100w, 200w" />  =>
<img src="path/hello.jpg" srcset="path/hello.jpg?w=100 100w, path/hello.jpg?w=200 200w" />

Description

NgOptimizedImage ensures that the loading of the Largest Contentful Paint (LCP) image is prioritized by:

• Automatically setting the fetchpriority attribute on the <img> tag
• Lazy loading non-priority images by default
• Asserting that there is a corresponding preconnect link tag in the document head

In addition, the directive:

• Generates appropriate asset URLs if a corresponding ImageLoader function is provided
• Automatically generates a srcset
• Requires that width and height are set
• Warns if width or height have been set incorrectly
• Warns if the image will be visually distorted when rendered

The NgOptimizedImage directive is marked as standalone and can be imported directly.

Follow the steps below to enable and use the directive:

1. Import it into the necessary NgModule or a standalone Component.
2. Optionally provide an ImageLoader if you use an image hosting service.
3. Update the necessary <img> tags in templates and replace src attributes with ngSrc. Using a ngSrc allows the directive to control when the src gets set, which triggers an image download.

Step 1: import the NgOptimizedImage directive.

import { NgOptimizedImage } from '@angular/common';

// Include it into the necessary NgModule
@NgModule({
  imports: [NgOptimizedImage],
})
class AppModule {}

// ... or a standalone Component
@Component({
  standalone: true
  imports: [NgOptimizedImage],
})
class MyStandaloneComponent {}

Step 2: configure a loader.

To use the default loader: no additional code changes are necessary. The URL returned by the generic loader will always match the value of "src". In other words, this loader applies no transformations to the resource URL and the value of the ngSrc attribute will be used as is.

To use an existing loader for a third-party image service: add the provider factory for your chosen service to the providers array. In the example below, the Imgix loader is used:

import {provideImgixLoader} from '@angular/common';

// Call the function and add the result to the `providers` array:
providers: [
  provideImgixLoader("https://my.base.url/"),
],

The NgOptimizedImage directive provides the following functions:

• provideCloudflareLoader
• provideCloudinaryLoader
• provideImageKitLoader
• provideImgixLoader

If you use a different image provider, you can create a custom loader function as described below.

To use a custom loader: provide your loader function as a value for the IMAGE_LOADER DI token.

import {IMAGE_LOADER, ImageLoaderConfig} from '@angular/common';

// Configure the loader using the `IMAGE_LOADER` token.
providers: [
  {
     provide: IMAGE_LOADER,
     useValue: (config: ImageLoaderConfig) => {
       return `https://example.com/${config.src}-${config.width}.jpg}`;
     }
  },
],

Step 3: update <img> tags in templates to use ngSrc instead of src.

<img ngSrc="logo.png" width="200" height="100">