assets

Elegant asset management for PHP with versioning, caching and providers for various storage backends

PHP

Nette Assets

Smart and simple way to work with static files in PHP applications

✅ automatic versioning for cache busting

✅ seamless Vite integration with HMR support

✅ lazy loading of file properties

✅ clean API for PHP and Latte templates

✅ multiple file sources support

Working with static files (images, CSS, JavaScript) in web applications often involves repetitive tasks: generating correct URLs, handling cache invalidation, managing file versions, and dealing with different environments. Nette Assets simplifies all of this.

Without Nette Assets:

{* You need to manually handle paths and versioning *}
<img src="/images/logo.png?v=2" width="100" height="50">
<link rel="stylesheet" href="/css/style.css?v=1699123456">

With Nette Assets:

{* Everything is handled automatically *}
{asset 'images/logo.png'}
{asset 'css/style.css'}

Installation

Install via Composer:

composer require nette/assets

Requirements: PHP 8.1 or higher.

Quick Start

Let’s start with the simplest possible example. You want to display an image in your application:

{* In your Latte template *}
{asset 'images/logo.png'}

This single line:

Finds your image file
Generates the correct URL with automatic versioning
Outputs a complete <img> tag with proper dimensions

That’s it! No configuration needed for basic usage. The library uses sensible defaults and works out of the box.

Custom HTML

Sometimes you need more control over the HTML:

{* Use n:asset when you want to control HTML attributes *}
<img n:asset="images/logo.png" alt="Company Logo" class="logo">

You can also get just the URL using the asset() function:

{* Get just the URL without HTML *}
<img src={asset('images/logo.png')} class="logo">

Using in PHP

In your presenters or services:

public function __construct(
	private Nette\Assets\Registry $assets
) {}

public function renderDefault(): void
{
	$logo = $this->assets->getAsset('images/logo.png');
	$this->template->logo = $logo;
}

Then in your template:

{asset $logo}
{* or *}
<img n:asset=$logo>
{* or *}
<img src={$logo} width={$logo->width} height={$logo->height} alt="Logo">

Basic Concepts

Before diving deeper, let’s understand three simple concepts that make Nette Assets powerful yet easy to use.

What is an Asset?

An asset is any static file in your application - images, stylesheets, scripts, fonts, etc. In Nette Assets, each file becomes an Asset object with useful properties:

$image = $assets->getAsset('photo.jpg');
echo $image->url;    // '/assets/photo.jpg?v=1699123456'
echo $image->width;  // 800
echo $image->height; // 600

Different file types have different properties. The library automatically detects the file type and creates the appropriate asset:

ImageAsset - Images with width, height, alternative text, and lazy loading support
ScriptAsset - JavaScript files with types and integrity hashes
StyleAsset - CSS files with media queries
AudioAsset - Audio files with duration information
VideoAsset - Video files with dimensions, duration, poster image, and autoplay settings
EntryAsset - Entry points with imports of styles and preloads of scripts
GenericAsset - Generic files with mime types

Where Assets Come From (Mappers)

A mapper is a service that knows how to find files and create URLs for them. The built-in FilesystemMapper does two things:

Looks for files in a specified directory
Generates public URLs for those files

You can have multiple mappers for different purposes:

The Registry - Your Main Entry Point

The Registry manages all your mappers and provides a simple API to get assets:

// Inject the registry
public function __construct(
	private Nette\Assets\Registry $assets
) {}

// Use it to get assets
$logo = $this->assets->getAsset('images/logo.png');

The registry is smart about which mapper to use:

// Uses the 'default' mapper
$css = $assets->getAsset('style.css');

// Uses the 'images' mapper (using prefix)
$photo = $assets->getAsset('images:photo.jpg');

// Uses the 'images' mapper (using array)
$photo = $assets->getAsset(['images', 'photo.jpg']);

Configuration

While Nette Assets works with zero configuration, you can customize it to match your project structure.

Zero Configuration

Without any configuration, Nette Assets expects all your static files to be in the assets folder within your public directory:

www/
├── assets/
│   └── logo.png
└── index.php

This creates a default mapper that:

Looks for files in %wwwDir%/assets
Generates URLs like /assets/file.ext

Minimal Configuration

The simplest configuration just tells the library where to find files:

assets:
	mapping:
		# This creates a filesystem mapper that:
		# - looks for files in %wwwDir%/assets
		# - generates URLs like /assets/file.ext
		default: assets

This is equivalent to the zero configuration setup but makes it explicit.

Setting Base Paths

By default, if you don’t specify base paths:

basePath defaults to %wwwDir% (your public directory)
baseUrl defaults to your project’s base URL (e.g., https://example.com/)

You can customize these to organize your static files under a common directory:

assets:
	# All mappers will resolve paths relative to this directory
	basePath: %wwwDir%/static

	# All mappers will resolve URL relative to this
	baseUrl: /static

	mapping:
		# Files in %wwwDir%/static/img, URLs like /static/img/photo.jpg
		default: img

		# Files in %wwwDir%/static/js, URLs like /static/js/app.js
		scripts: js

Advanced Configuration

For more control, you can configure each mapper in detail:

assets:
	mapping:
		# Simple format - creates FilesystemMapper looking in 'img' folder
		images: img

		# Detailed format with additional options
		styles:
			path: css                   # Directory to search for files
			extension: css              # Always add .css extension to requests

		# Different URL and directory path
		audio:
			path: audio                 # Files stored in 'audio' directory
			url: https://static.example.com/audio  # But served from CDN

		# Custom mapper service (dependency injection)
		cdn: @cdnMapper

The path and url can be:

Relative: resolved from %wwwDir% (or basePath) and project base URL (or baseUrl)
Absolute: used as-is (/var/www/shared/assets, https://cdn.example.com)

Manual Configuration (Without Nette Framework)

If you’re not using the Nette Framework or prefer to configure everything manually in PHP:

use Nette\Assets\Registry;
use Nette\Assets\FilesystemMapper;

// Create registry
$registry = new Registry;

// Add mappers manually
$registry->addMapper('default', new FilesystemMapper(
	baseUrl: 'https://example.com/assets',   // URL prefix
	basePath: __DIR__ . '/assets',           // Filesystem path
	extensions: ['webp', 'jpg', 'png'],      // Try WebP first, fallback to JPG/PNG
	versioning: true
));

// Use the registry
$logo = $registry->getAsset('logo');  // Finds logo.webp, logo.jpg, or logo.png
echo $logo->url;

For more advanced configuration options using NEON format without the full Nette Framework, install the configuration component:

composer require nette/bootstrap

Then you can use NEON configuration files as described in the Nette Bootstrap documentation.

Working with Assets

Let’s explore how to work with assets in your PHP code.

Basic Retrieval

The Registry provides two methods for getting assets:

// This throws Nette\Assets\AssetNotFoundException if file doesn't exist
try {
	$logo = $assets->getAsset('images/logo.png');
	echo $logo->url;
} catch (AssetNotFoundException $e) {
	// Handle missing asset
}

// This returns null if file doesn't exist
$banner = $assets->tryGetAsset('images/banner.jpg');
if ($banner) {
	echo $banner->url;
}

Specifying Mappers

You can explicitly choose which mapper to use:

// Use default mapper
$asset = $assets->getAsset('document.pdf');

// Use specific mapper using prefix with colon
$asset = $assets->getAsset('images:logo.png');

// Use specific mapper using array syntax
$asset = $assets->getAsset(['images', 'logo.png']);

Asset Types and Properties

The library automatically detects file types and provides relevant properties:

// Images
$image = $assets->getAsset('photo.jpg');
echo $image->width;   // 1920
echo $image->height;  // 1080
echo $image->url;     // '/assets/photo.jpg?v=1699123456'

// All assets can be cast to string (returns URL)
$url = (string) $assets->getAsset('document.pdf');

Lazy Loading of Properties

Properties like image dimensions, audio duration, or MIME types are retrieved only when accessed. This keeps the library fast:

$image = $assets->getAsset('photo.jpg');
// No file operations yet

echo $image->url;    // Just returns URL, no file reading

echo $image->width;  // NOW it reads the file header to get dimensions
echo $image->height; // Already loaded, no additional file reading

// For MP3 files, duration is estimated (most accurate for Constant Bitrate files)
$audio = asset('audio:episode-01.mp3');
echo $audio->duration; // in seconds

// Even generic assets lazy-load their MIME type
$file = $assets->getAsset('document.pdf');
echo $file->mimeType; // Now it detects: 'application/pdf'

Working with Options

Mappers can support additional options to control their behavior. For example, the FilesystemMapper supports the version option:

// Disable versioning for specific asset
$asset = $assets->getAsset('style.css', ['version' => false]);
echo $asset->url;  // '/assets/style.css' (no ?v=... parameter)

Different mappers may support different options. Custom mappers can define their own options to provide additional functionality.

Latte Integration

Nette Assets shines in Latte templates with intuitive tags and functions.

Basic Usage with `{asset}` Tag

The {asset} tag renders complete HTML elements:

{* Renders: <img src="/assets/hero.jpg?v=123" width="1920" height="1080"> *}
{asset 'images/hero.jpg'}

{* Renders: <script src="/assets/app.js?v=456"></script> *}
{asset 'scripts/app.js'}

{* Renders: <link rel="stylesheet" href="/assets/style.css?v=789"> *}
{asset 'styles/style.css'}

{* Any additional parameters are passed as asset options *}
{asset 'style.css', version: false}

The tag automatically:

Detects the asset type from file extension
Generates the appropriate HTML element
Adds versioning for cache busting
Includes dimensions for images

However, if you use the {asset} tag inside an HTML attribute, it will only output the URL:

<div style="background-image: url({asset 'images/bg.jpg'})">
	Content
</div>

<img srcset="{asset 'images/[email protected]'} 2x">

Using Specific Mappers

Just like in PHP, you can specify which mapper to use:

{* Uses the 'images' mapper (via prefix) *}
{asset 'images:product-photo.jpg'}

{* Uses the 'images' mapper (via array syntax) *}
{asset ['images', 'product-photo.jpg']}

Custom HTML with `n:asset` Attribute

When you need control over the HTML attributes:

{* The n:asset attribute fills in the appropriate attributes *}
<img n:asset="images:product.jpg" alt="Product Photo" class="rounded shadow">

{* Works with any relevant HTML element *}
<a n:asset="images:product.jpg">link to image</a>
<script n:asset="scripts/analytics.js" defer></script>
<link n:asset="styles/print.css" media="print">
<audio n:asset="podcast.mp3" controls></audio>
<video n:asset="podcast.avi"></video>

The n:asset attribute:

Sets src for images, scripts, and audio/video
Sets href for stylesheets and preload links
Adds dimensions for images and other attributes
Preserves all your custom attributes

How to use a variable in n:asset?

{* The variable can be written quite simply *}
<img n:asset="$post->image">

{* Use curly brackets when specifying the mapper *}
<img n:asset="media:{$post->image}">

{* Or you can use array notation *}
<img n:asset="[images, $post->image]">

{* You can pass options for assets *}
<link n:asset="styles/print.css, version: false" media="print">

Getting Just URLs with Functions

For maximum flexibility, use the asset() function:

{var $logo = asset('images/logo.png')}
<img src={$logo} width={$logo->width} height={$logo->height}>

Handling Optional Assets

You can use optional tags that won’t throw exceptions if the asset is missing:

{* Optional asset tag - renders nothing if asset not found *}
{asset? 'images/optional-banner.jpg'}

{* Optional n:asset attribute - skips the attribute if asset not found *}
<img n:asset?="images/user-photo.jpg" alt="User Photo" class="avatar">

The optional variants ({asset?} and n:asset?) silently skip rendering when the asset doesn’t exist, making them perfect for optional images, dynamic content, or situations where missing assets shouldn’t break your layout.

For maximum flexibility, use the tryAsset() function:

{var $banner = tryAsset('images/summer-sale.jpg')}
{if $banner}
	<div class="banner">
		<img src={$banner} alt="Summer Sale">
	</div>
{/if}

{* Or with a fallback *}
<img n:asset="tryAsset('user-avatar.jpg') ?? asset('default-avatar.jpg')" alt="Avatar">

Performance Optimization with Preloading

Improve page load performance by preloading critical assets:

{* In your <head> section *}
{preload 'styles/critical.css'}
{preload 'fonts/heading.woff2'}

Generates:

<link rel="preload" href="/assets/styles/critical.css?v=123" as="style">
<link rel="preload" href="/assets/fonts/heading.woff2" as="font" crossorigin>

The {preload} tag automatically:

Determines the correct as attribute
Adds crossorigin for fonts
Uses modulepreload for ES modules

Advanced Features

Extension Autodetection

When you have multiple formats of the same asset, the built-in FilesystemMapper can automatically find the right one:

assets:
	mapping:
		images:
			path: img
			extension: [webp, jpg, png]  # Check for each extension in order

Now when you request an asset without extension:

{* Automatically finds: logo.webp, logo.jpg, or logo.png *}
{asset 'images:logo'}

This is useful for:

Progressive enhancement (WebP with JPEG fallback)
Flexible asset management
Simplified templates

You can also make extension optional:

assets:
	mapping:
		scripts:
			path: js
			extension: [js, '']  # Try with .js first, then without

Asset Versioning

Browser caching is great for performance, but it can prevent users from seeing updates. Asset versioning solves this problem.

The FilesystemMapper automatically adds version parameters based on file modification time:

{asset 'css/style.css'}
{* Output: <link rel="stylesheet" href="/css/style.css?v=1699123456"> *}

When you update the CSS file, the timestamp changes, forcing browsers to download the new version.

You can disable versioning at multiple levels:

assets:
	# Global versioning setting (defaults to true)
	versioning: false

	mapping:
		default:
			path: assets
			# Enable versioning for this mapper only
			versioning: true

Or per asset using asset options:

// In PHP
$asset = $assets->getAsset('style.css', ['version' => false]);

// In Latte
{asset 'style.css', version: false}

Working with Fonts

Font assets support preloading with proper CORS attributes:

{* Generates proper preload with crossorigin attribute *}
{preload 'fonts:OpenSans-Regular.woff2'}

{* In your CSS *}
<style>
	@font-face {
		font-family: 'Open Sans';
		src: url('{asset 'fonts:OpenSans-Regular.woff2'}') format('woff2');
		font-display: swap;
	}
</style>

Vite Integration

For modern JavaScript applications, Nette Assets includes a specialized ViteMapper that integrates with Vite’s build process.

Basic Setup

Create a vite.config.ts file in your project root. This file tells Vite where to find your source files and where to put the compiled ones.

import { defineConfig } from 'vite';
import nette from '@nette/vite-plugin';

export default defineConfig({
	build: {
		rollupOptions: {
			input: 'assets/app.js', // entry point
		},
	},
	plugins: [nette()],
});

Configure the ViteMapper in your NEON file by setting type: vite:

assets:
	mapping:
		default:
			type: vite
			path: assets

Development Mode

The Vite dev server provides instant updates without page reload:

npm run dev

Assets are automatically served from the Vite dev server when:

Your app is in debug mode
The dev server is running (auto-detected)

No configuration needed - it just works!

Production Mode

npm run build

Vite creates optimized, versioned bundles that Nette Assets serves automatically.

Understanding Entry Points and Dependencies

When you build a modern JavaScript application, your bundler (like Vite) often splits code into multiple files for better performance. An “entry point” is your main JavaScript file that imports other modules.

For example, your src/main.js might:

Import a CSS file
Import vendor libraries (like Vue or React)
Import your application components

Vite processes this and generates:

The main JavaScript file
Extracted CSS file(s)
Vendor chunks for better caching
Dynamic imports for code splitting

The EntryAsset class handles this complexity.

Rendering Entry Points

The {asset} tag automatically handles all dependencies.

{asset 'vite:src/main.js'}

Single tag renders everything needed for that entry point:

<!-- Main entry point -->
<script src="/build/assets/main-4a8f9c7.js" type="module" crossorigin></script>

<!-- Vendor chunk preload -->
<link rel="modulepreload" href="/build/assets/vendor-8c7fa9b.js" crossorigin>

<!-- Extracted CSS -->
<link rel="stylesheet" href="/build/assets/main-2b9c8d7.css" crossorigin>

Large applications often have multiple entry points with shared dependencies. Vite automatically deduplicates shared chunks.

Development vs Production Example

The ViteMapper automatically switches between development and production modes:

During Development:

{* Serves from Vite dev server with hot module replacement *}
{asset 'vite:src/main.js'}
{* Output for example:
	<script src="https://localhost:5173/@vite/client" type="module"></script>
	<script src="https://localhost:5173/src/main.js" type="module"></script>
*}

In Production:

{* Serves built files with hashed names from manifest *}
{asset 'vite:src/main.js'}
{* Output for example:
	<script src="https://example.com/assets/main-1a2b3c4d.js" type="module" crossorigin></script>
	<link rel="stylesheet" href="https://example.com/assets/main-a1b2c3d4.css" crossorigin>
*}

Versioning in Vite

Vite handles the entry point versioning itself and can be set in its configuration file. Unlike FilesystemMapper, Vite by default includes a hash in the filename (main-4a8f9c7.js). This approach works better with JavaScript module imports.

Fallback to Filesystem

If a file isn’t found in the Vite manifest, ViteMapper will attempt to find it directly on the filesystem, similar to how FilesystemMapper works. This is particularly useful for files in Vite’s publicDir (default: public/), which are copied as-is to the output directory without being processed or included in the manifest.

Code Splitting and Dynamic Imports

When your application uses dynamic imports:

// In your JavaScript
if (condition) {
	import('./features/special-feature.js').then(module => {
		module.init();
	});
}

Nette Assets does not automatically preload dynamic imports - this is intentional as preloading all possible dynamic imports could hurt performance.

If you want to preload specific dynamic imports, you can do so explicitly:

{* Manually preload critical dynamic imports *}
{preload 'vite:features/special-feature.js'}

This gives you fine-grained control over which resources are preloaded based on your application’s needs.

Creating Custom Mappers

While the built-in FilesystemMapper and ViteMapper handle most use cases, you might need custom asset resolution for:

Cloud storage (S3, Google Cloud)
Database-stored files
Dynamic asset generation
Third-party CDN integration

The Mapper Interface

All mappers implement a simple interface:

interface Mapper
{
	/**
	 * @throws Nette\Assets\AssetNotFoundException
	 */
	public function getAsset(string $reference, array $options = []): Nette\Assets\Asset;
}

The contract is straightforward:

Take a reference (like “logo.png” or “reports/annual-2024.pdf”)
Return an Asset object
Throw AssetNotFoundException if the asset doesn’t exist

Creating Assets with Helper

The Nette\Assets\Helpers::createAssetFromUrl() method is your primary tool for creating Asset objects in custom mappers. This helper automatically chooses the appropriate asset class based on the file’s extension:

public static function createAssetFromUrl(
	string $url,           // The public URL of the asset
	?string $path = null,  // Optional local file path (for reading properties)
	array $args = []       // Additional constructor arguments
): Asset

The helper automatically creates the appropriate asset class:

ScriptAsset for JavaScript files (application/javascript)
StyleAsset for CSS files (text/css)
ImageAsset for image files (image/*)
AudioAsset for audio files (audio/*)
VideoAsset for video files (video/*)
FontAsset for font files (font/woff, font/woff2, font/ttf)
GenericAsset for everything else

Database Mapper Example

For applications storing file metadata in a database:

class DatabaseMapper implements Mapper
{
	public function __construct(
		private Connection $db,
		private string $baseUrl,
		private Storage $storage,
	) {}

	public function getAsset(string $reference, array $options = []): Asset
	{
		// Find asset in database
		$row = $this->db->fetchRow('SELECT * FROM assets WHERE id = ?', $reference);
		if (!$row) {
			throw new AssetNotFoundException("Asset '$reference' not found in database");
		}

		$url = $this->baseUrl . '/file/' . $row->storage_path;
		$localPath = $this->storage->getLocalPath($row->storage_path);

		return Helpers::createAssetFromUrl(
			url: $url,
			path: $localPath,
			args: [
				'mimeType' => $row->mime_type,
				'width' => $row->width,
				'height' => $row->height,
			]
		);
	}
}

assets:
	mapping:
		db: DatabaseMapper(...)

Cloud Storage Mapper

For S3 or Google Cloud Storage:

class S3Mapper implements Mapper
{
	public function __construct(
		private S3Client $s3,
		private string $bucket,
		private string $region,
		private bool $private = false
	) {}

	public function getAsset(string $reference, array $options = []): Asset
	{
		try {
			// Check if object exists
			$this->s3->headObject([
				'Bucket' => $this->bucket,
				'Key' => $reference,
			]);

			if ($this->private) {
				// Generate presigned URL for private files
				$url = $this->s3->createPresignedRequest(
					$this->s3->getCommand('GetObject', [
						'Bucket' => $this->bucket,
						'Key' => $reference,
					]),
					'+10 minutes'
				)->getUri();
			} else {
				// Public URL
				$url = "https://s3.{$this->region}.amazonaws.com/{$this->bucket}/{$reference}";
			}

			return Helpers::createAssetFromUrl($url);

		} catch (S3Exception $e) {
			throw new AssetNotFoundException("Asset '$reference' not found in S3");
		}
	}
}

Using Options

Options allow users to modify mapper behavior on a per-asset basis. This is useful when you need different transformations, sizes, or processing for the same asset:

public function getAsset(string $reference, array $options = []): Asset
{
	$thumbnail = $options['thumbnail'] ?? null;

	$url = $thumbnail
		? $this->cdnUrl . '/thumb/' . $reference
		: $this->cdnUrl . '/' . $reference;

	return Helpers::createAssetFromUrl($url);
}

Usage:

// Get normal image
$photo = $assets->getAsset('cdn:photo.jpg');

// Get thumbnail version
$thumbnail = $assets->getAsset('cdn:photo.jpg', ['thumbnail' => true]);

// In Latte: {asset 'cdn:photo.jpg', thumbnail: true}

This pattern is useful for:

Image transformations (thumbnails, different sizes)
CDN parameters (quality, format conversion)
Access control (signed URLs, expiration times)

Handle Multiple Sources

Sometimes you need to check multiple locations for an asset. A fallback mapper can try different sources in order:

class FallbackMapper implements Mapper
{
	public function __construct(
		private array $mappers
	) {}

	public function getAsset(string $reference, array $options = []): Asset
	{
		foreach ($this->mappers as $mapper) {
			try {
				return $mapper->getAsset($reference, $options);
			} catch (AssetNotFoundException) {
				// continue
			}
		}

		throw new AssetNotFoundException("Asset '$reference' not found in any source");
	}
}