Frontend Build System

Complete reference for Frappe's frontend asset bundling pipeline, from build configuration to production optimization.

Versions: v14 (build.json) / v15+ (esbuild)

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Quick Reference: Build Commands

Task	Command
Build all apps	bench build
Build specific app	bench build --app myapp
Build multiple apps	bench build --apps frappe,erpnext
Production build (minified)	bench build --production
Force rebuild	bench build --force
Watch mode (auto-rebuild)	bench watch
Hard link assets	bench build --hard-link

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Decision Tree: Build System Selection

Which build system?
├── Frappe v14?
│   └── build.json — Concatenation-based bundling
├── Frappe v15+?
│   └── esbuild — ES module bundling with *.bundle.* convention
└── Migrating v14 → v15?
    └── Replace build.json with *.bundle.* files in public/

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Build Pipeline Overview

v15+ (esbuild): Current System

The v15+ build system uses esbuild for fast ES module bundling. It automatically discovers bundle entry points by scanning the public/ directory for files matching *.bundle.{js|ts|css|scss|sass|less|styl}.

How it works:

1. bench build scans each app's public/ directory recursively
2. Files matching *.bundle.* are treated as entry points
3. esbuild compiles, bundles, and optionally minifies each entry point
4. Output goes to assets/dist/[app]/js/ or assets/dist/[app]/css/
5. Filenames include content hashes for cache-busting: main.bundle.HASH.js

Supported file types:

• .js — ES6 modules with import/export
• .ts — TypeScript
• .vue — Vue single-file components
• .css — Standard CSS
• .scss / .sass — SASS/SCSS stylesheets
• .less — Less stylesheets
• .styl — Stylus stylesheets

v14 (build.json): Legacy System

The v14 system uses build.json in the app root to define concatenation rules.

{
  "js/myapp.min.js": [
    "public/js/file1.js",
    "public/js/file2.js"
  ],
  "css/myapp.min.css": [
    "public/css/style1.css",
    "public/css/style2.css"
  ]
}

NEVER use build.json in v15+ — it is ignored by the esbuild pipeline.

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Bundle Entry Points [v15+]

Creating a Bundle

Place files in your app's public/ directory with the .bundle. naming convention:

myapp/
└── public/
    ├── js/
    │   └── myapp.bundle.js       # → dist/myapp/js/myapp.bundle.HASH.js
    ├── css/
    │   └── myapp.bundle.scss     # → dist/myapp/css/myapp.bundle.HASH.css
    └── components/
        └── widget.bundle.js      # → dist/myapp/js/widget.bundle.HASH.js

Bundle File Content

// myapp/public/js/myapp.bundle.js
import { createApp } from "vue";
import MyComponent from "./components/MyComponent.vue";

// ES6 imports are resolved by esbuild
import "../css/myapp.bundle.scss";

// npm packages (installed via yarn) can be imported directly
import dayjs from "dayjs";

createApp(MyComponent).mount("#myapp-root");

Output Mapping

Input	Output
public/js/main.bundle.js	assets/dist/[app]/js/main.bundle.[hash].js
public/css/style.bundle.scss	assets/dist/[app]/css/style.bundle.[hash].css
public/deep/nested/file.bundle.ts	assets/dist/[app]/js/file.bundle.[hash].js

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hooks.py Asset Inclusion

Desk Assets (Backend Interface)

# hooks.py — loads in /app (Desk)
app_include_js = "myapp.bundle.js"
app_include_css = "myapp.bundle.css"

# Multiple files
app_include_js = ["myapp.bundle.js", "extra.bundle.js"]
app_include_css = ["myapp.bundle.css", "extra.bundle.css"]

Portal Assets (Public Website)

# hooks.py — loads on web pages (portal)
web_include_js = "myapp-web.bundle.js"
web_include_css = "myapp-web.bundle.css"

Page-Specific Assets

# hooks.py — loads on specific Desk pages
page_js = {"page_name": "public/js/custom_page.js"}

Web Form Assets (Standard Web Forms Only)

# hooks.py — loads on specific Web Forms
webform_include_js = {"ToDo": "public/js/custom_todo.js"}
webform_include_css = {"ToDo": "public/css/custom_todo.css"}

Critical Rules

• ALWAYS use the bundle filename (not the full path) in hooks.py for v15+
• NEVER include the hash in hooks.py — Frappe resolves the hashed filename automatically
• ALWAYS rebuild after changing hooks.py: bench build --app myapp
• Multiple apps can define the same hooks — assets accumulate across all installed apps

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Including Assets in Templates

Jinja Helpers

<!-- Include script with correct hash -->
{{ include_script("myapp.bundle.js") }}

<!-- Include stylesheet with correct hash -->
{{ include_style("myapp.bundle.css") }}

<!-- Get path string only (no HTML tag) -->
<script src="{{ bundled_asset('myapp.bundle.js') }}"></script>

Lazy Loading in Desk

// Load asset on demand (returns Promise)
frappe.require("myapp.bundle.js", () => {
    // Asset loaded, initialize component
    myapp.init();
});

// Multiple assets
frappe.require(["widget.bundle.js", "widget.bundle.css"], () => {
    // Both loaded
});

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SCSS/CSS Compilation

SCSS Bundle Example

// myapp/public/css/myapp.bundle.scss

// Import Frappe variables (available in all apps)
@import "frappe/public/scss/variables";

// Import partials (NOT bundles — no .bundle. in name)
@import "./components/header";
@import "./components/sidebar";

.myapp-container {
  padding: var(--padding-lg);
  background: var(--bg-color);
}

Partial Files

Partials (files starting with _ or without .bundle. in the name) are NOT compiled as entry points. They are only included via @import:

public/css/
├── myapp.bundle.scss        # Entry point — compiled
├── _variables.scss          # Partial — imported only
└── components/
    ├── _header.scss         # Partial — imported only
    └── _sidebar.scss        # Partial — imported only

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Development Workflow

Watch Mode [v15+]

# Auto-rebuild on file changes
bench watch

• Watches all apps' public/ directories for changes
• Rebuilds only affected bundles (incremental)
• Desk auto-reloads when assets change (if live_reload is enabled)

Enabling Live Reload

# Via config
bench set-config -g live_reload true

# Via environment variable
export LIVE_RELOAD=1

Development vs Production Build

Feature	Development (bench build)	Production (bench build --production)
Minification	No	Yes
Source maps	Yes	No
Bundle size	Larger	Optimized
Build speed	Fast	Slower

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Frappe UI (Vue.js) Custom Pages [v15+]

Setting Up a Vue Page

// myapp/public/js/mypage.bundle.js
import { createApp } from "vue";
import { FrappeUI } from "frappe-ui";
import App from "./App.vue";

const app = createApp(App);
app.use(FrappeUI);
app.mount("#myapp-page");

Registering the Page

# Create a Page DocType or use www/ for web pages
# The bundle loads via hooks.py or include_script()

npm Dependencies

# Install from app directory
cd apps/myapp
yarn add vue frappe-ui dayjs

Dependencies are resolved by esbuild from node_modules/ during build.

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Common Build Errors and Fixes

Error: "Could not resolve module"

ERROR: Could not resolve "some-package"

Fix: Install the missing npm package:

cd apps/myapp && yarn add some-package

Error: "No bundle entry points found"

Fix: Ensure files use the *.bundle.* naming convention and are in the public/ directory.

Error: Stale Assets After Deployment

Fix: Force rebuild with cache clear:

bench build --force
bench clear-cache

Error: CSS Not Updating

Fix: Check that SCSS files import correctly and the entry point has .bundle. in the name:

bench build --app myapp --force

Error: "build.json" Ignored in v15

Fix: Migrate to *.bundle.* entry points. build.json is a v14-only feature.

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Asset Optimization for Production

Pre-Deployment Checklist

1. Build with production flag: bench build --production
2. Verify bundle sizes: Check assets/dist/ for unexpectedly large files
3. Use lazy loading: Split rarely-used features into separate bundles loaded via frappe.require()
4. Minimize hook includes: Only include essential assets in app_include_js/css
5. Use CSS variables: Leverage Frappe's built-in CSS custom properties instead of duplicating styles

Bundle Splitting Strategy

public/
├── js/
│   ├── myapp.bundle.js          # Core — loaded on every page via hooks
│   ├── report-widget.bundle.js  # Lazy — loaded only on report pages
│   └── chart-tools.bundle.js    # Lazy — loaded only when charts needed
└── css/
    ├── myapp.bundle.scss        # Core — loaded on every page via hooks
    └── print.bundle.scss        # Lazy — loaded only for print views

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Version Differences

Feature	v14	v15+
Build system	build.json	esbuild
Entry point convention	Defined in JSON	*.bundle.* auto-discovery
TypeScript support	No	Yes
Vue SFC support	No	Yes
SCSS compilation	Via build pipeline	Via esbuild
Watch mode	bench watch	bench watch (faster)
Live reload	Manual	Automatic (configurable)
Source maps	Limited	Full support
Tree shaking	No	Yes
npm imports	Requires manual bundling	Direct ES6 imports

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Reference Files

File	Contents
examples.md	Complete build configuration examples
anti-patterns.md	Common build mistakes and fixes