Magento 2 Frontend Development

Before writing code

Fetch live docs:

1. Web-search site:developer.adobe.com commerce frontend-core for frontend development guide
2. Fetch https://developer.adobe.com/commerce/frontend-core/guide/css/preprocess for CSS/LESS docs
3. Web-search site:developer.adobe.com commerce frontend-core guide layouts for layout XML reference
4. Web-search site:developer.adobe.com commerce frontend-core guide templates for template guide

Layout XML

How Layouts Work

Layout files map to route handles and define the page structure:

• Containers — structural wrappers (header, content, footer)
• Blocks — content-rendering units tied to PHP classes and templates
• Handle naming: <route>_<controller>_<action>.xml (e.g., catalog_product_view.xml)
• default.xml — applies to all pages

Key Layout Instructions

• <referenceContainer> — modify an existing container
• <referenceBlock> — modify an existing block
• <block> — add a new block with class, template, name
• <move> — relocate a block/container
• <referenceBlock name="block_name" remove="true"/> — remove a block (or use <referenceContainer> for containers). Note: there is no standalone <remove> element for blocks; the remove="true" attribute is set on <referenceBlock> or <referenceContainer>.
• <update> — include another layout handle
• <arguments> — pass data to blocks

Layout Files Location

• Module: view/frontend/layout/ or view/adminhtml/layout/
• Theme: Magento_Module/layout/

Blocks and Templates

Block Classes

• Extend Magento\Framework\View\Element\Template
• Contain data logic that templates consume
• $block->someMethod() in PHTML templates

PHTML Templates

• Located in view/frontend/templates/ or theme overrides
• PHP + HTML files with .phtml extension
• Access block: $block, escape output: $escaper->escapeHtml()

ViewModels (Recommended)

MVVM pattern — inject ViewModels into blocks via layout XML arguments:

• ViewModels implement Magento\Framework\View\Element\Block\ArgumentInterface
• Keeps blocks thin; ViewModels carry the logic
• Access in template: $viewModel = $block->getData('view_model');

JavaScript

RequireJS

• AMD module system — all JS loaded as modules
• requirejs-config.js — maps module aliases, mixins, shims
• Located in view/frontend/web/ or view/frontend/requirejs-config.js

KnockoutJS

• Two-way data binding for dynamic UI
• Used extensively in checkout and UI components
• Custom bindings via ko.bindingHandlers
• HTML templates in view/frontend/web/template/ (.html files)

JS Mixins

Extend existing JS modules without overriding:

• Declared in requirejs-config.js under config.mixins
• Wrapper function receives original module and modifies it

jQuery Widgets

Custom widgets extend $.widget:

• Initialized via data-mage-init attribute or <script type="text/x-magento-init">
• Configuration passed as JSON

Themes

Theme Structure

app/design/frontend/VendorName/theme-name/
├── etc/view.xml              # Image sizes, responsive breakpoints
├── registration.php          # Theme registration
├── theme.xml                 # Theme name, parent
├── composer.json
├── Magento_Module/           # Module overrides
│   ├── layout/               # Layout XML overrides
│   └── templates/            # Template overrides
├── web/
│   ├── css/source/           # LESS source files
│   ├── images/
│   └── js/
└── media/preview.jpg

Theme Inheritance

Themes declare a parent in theme.xml. Fallback chain: current theme → parent theme → module views → framework. Override files by placing them in the same relative path.

Hyva Themes (Modern Alternative)

Open source since late 2025. Replaces KnockoutJS + RequireJS + jQuery with Alpine.js + Tailwind CSS. Dramatically faster: ~5 requests vs ~230, ~0.4MB vs ~3MB page weight.

LESS/CSS

• Default preprocessor: LESS
• @magento_import directive for theme fallback
• Variables in _variables.less, overridden per theme
• Server-side compilation for production, client-side for development

Best Practices

• Use ViewModels instead of heavy block classes
• Override templates at the theme level, not module level (for customization)
• Use layout XML to add/move/remove blocks — avoid direct template editing of core
• Minimize JavaScript — prefer server-rendered HTML where possible
• Use $escaper->escapeHtml(), escapeUrl(), escapeJs() for XSS prevention
• Consider Hyva for new projects — dramatically better performance

Fetch the frontend development guide for exact layout XML schema, template escaping methods, and RequireJS configuration patterns before implementing.