@angular/common

NgOptimizedImage

directive

stable

Directive that improves image loading performance by enforcing best practices.

API

    
      class NgOptimizedImage implements OnInit ,OnChanges {}

ngSrc

string

Name of the source image. Image name will be processed by the image loader and the final URL will be applied as the src property of the image.

ngSrcset

string

A comma separated list of width or density descriptors. The image name will be taken from ngSrc and combined with the list of width or density descriptors to generate the final srcset property of the image.

Example:

<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" />

sizes

string | undefined

The base sizes attribute passed through to the <img> element. Providing sizes causes the image to create an automatic responsive srcset.

width

number | undefined

For responsive images: the intrinsic width of the image in pixels. For fixed size images: the desired rendered width of the image in pixels.

height

number | undefined

For responsive images: the intrinsic height of the image in pixels. For fixed size images: the desired rendered height of the image in pixels.

decoding

"auto" | "sync" | "async" | undefined

The desired decoding behavior for the image. Defaults to auto if not explicitly set, matching native browser behavior.

Use async to decode the image off the main thread (non-blocking), sync for immediate decoding (blocking), or auto to let the browser decide the optimal strategy.

Spec

loading

"auto" | "lazy" | "eager" | undefined

The desired loading behavior (lazy, eager, or auto). Defaults to lazy, which is recommended for most images.

Warning: Setting images as loading="eager" or loading="auto" marks them as non-priority images and can hurt loading performance. For images which may be the LCP element, use the priority attribute instead of loading.

priority

boolean

Indicates whether this image should have a high priority.

loaderParams

{ [key: string]: any; } | undefined

Data to pass through to custom loaders.

disableOptimizedSrcset

boolean

Disables automatic srcset generation for this image.

fill

boolean

Sets the image to "fill mode", which eliminates the height/width requirement and adds styles such that the image fills its containing element.

placeholder

string | boolean | undefined

A URL or data URL for an image to be used as a placeholder while this image loads.

placeholderConfig

ImagePlaceholderConfig | undefined

Configuration object for placeholder settings. Options:

blur: Setting this to false disables the automatic CSS blur.

generatePlaceholder

string | boolean | null

Returns an image url formatted for use with the CSS background-image property. Expects one of:

A base64 encoded image, which is wrapped and passed through.
A boolean. If true, calls the image loader to generate a small placeholder url.

@paramplaceholderInputstring | boolean

@returnsstring | boolean | null

shouldBlurPlaceholder

boolean

Determines if blur should be applied, based on an optional boolean property blur within the optional configuration object placeholderConfig.

@paramplaceholderConfigImagePlaceholderConfig | undefined

@returnsboolean

Description

Directive that improves image loading performance by enforcing best practices.

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
Automatically generating a 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

Usage Notes

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

Follow the steps below to enable and use the directive:

Import it into the necessary NgModule or a standalone Component.
Optionally provide an ImageLoader if you use an image hosting service.
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({  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:

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">