dj - Dynamic JS File Extractor

中文 | English

dj intelligently detects dynamically loaded JavaScript files by statically analyzing website HTML and JS code, including webpack chunks, import() lazy loading, and more.

Features

• Deep analysis of website HTML and JS to extract dynamically loaded JavaScript files
• Smart detection of dynamic loading patterns: import(), require(), webpack chunks, vite preload, etc.
• Support for multiple frontend framework chunk mappings: Next.js, Nuxt.js, Vite, SvelteKit, Webpack, and more
• Automatic Source Map discovery
• Custom User-Agent and proxy support
• Multiple output formats: text, JSON, markdown

Installation

go install (recommended)

go install github.com/ejfkdev/dj@latest

Build from source

git clone https://github.com/ejfkdev/dj.git
cd dj
go build -ldflags="-X main.version=1.0.0" -o dj .

Download prebuilt binaries

Visit the Releases page to download binaries for your platform.

Usage

dj [options] <URL>

Basic usage

# Extract JS URLs (real-time output)
dj https://example.com

# Output in JSON format
dj -f json https://example.com

# Output in Markdown format
dj -f md https://example.com

Command line options

Option	Description
--debug	Enable debug output
-f <format>	Output format: text (default), json, md
--cache	Enable caching (enabled by default)
--cache=false	Disable caching
--useragent=<UA>	Custom User-Agent string
--proxy=<URL>	HTTP proxy URL
-h	Show help information

Examples

# Custom User-Agent
dj --useragent="Mozilla/5.0 (iPhone; CPU iPhone OS 14_0 like Mac OS X) ..." https://example.com

# Use proxy
dj --proxy="http://127.0.0.1:7890" https://example.com

# Enable debug mode
dj --debug https://example.com

Tested websites

Website	JS Count
docs.qq.com	~3270
vue.ruoyi.vip	~68
gitee.com	~63
nuxt.com.cn	~160
chat.z.ai	~539
show.cool-admin.com/login	~120
demo.1panel.cn	~161
mail.qq.com	~418
chat.deepseek.com	~634

dj https://docs.qq.com
dj https://vue.ruoyi.vip
dj https://gitee.com
dj https://nuxt.com.cn
dj https://chat.z.ai
dj https://show.cool-admin.com/login
dj https://demo.1panel.cn

Supported patterns and frameworks (16 plugins)

Framework/Tool	Features
HTMLScript	Parse <script src> tags to extract directly referenced JS
DynamicImport	import() dynamic loading, import(/* webpackChunkName */) comments
Webpack	__webpack_require__.e() dynamic loading, chunk map detection, webpackChunk global, string chunk ID mapping
Next.js	App Router / Pages Router chunk detection, build manifest, flight chunk
Nuxt.js	/_nuxt/ path pattern, build assets
Vite	__vitePreload(), modulepreload, lazy loading chunks
SvelteKit	/_app/immutable/nodes/ and /_app/immutable/chunks/ paths
RequireJS	require() / define() dependency loading, data-main
Module Federation	__webpack_require__.federation remote modules, manifest.json parsing
ModuleFederationManifest	Module Federation manifest.json shared/exposes module extraction
HelMicro	metadata.json component config, CDN prefix
ESMImport	Static import declaration extraction
ScriptCreate	document.createElement('script') dynamic loading
ModernJS	ByteDance ModernJS route manifest, b.p publicPath
URLPattern	General URL pattern matching and path probing
SourceMap	.map file detection (via sourceMappingURL, HTTP header, or inline data URI)

How it works

1. Download the target webpage HTML
2. Launch plugin analysis - each URL is processed concurrently by a goroutine:
   • Download JS content
   • Detect Content-Type (skip static resources returning HTML)
   • Dispatch to all plugins for pattern matching
3. Plugins discover new JS URLs or path fragments, add to processing queue
4. Probe for Source Map files (via sourceMappingURL or HTTP header)
5. Collect all discovered JS URLs and output

Output formats

Text (default)

https://example.com/js/main.js
https://example.com/js/chunk-abc123.js
https://example.com/js/async-def456.js

JSON

{
  "summary": {
    "jsCount": 3,
    "sourceMapCount": 1
  },
  "jsURLs": [
    "https://example.com/js/main.js",
    "https://example.com/js/chunk-abc123.js"
  ],
  "cacheBase": "/tmp/ejfkdev/dj/example.com",
  "cacheDirs": {
    "js": "/tmp/ejfkdev/dj/example.com/js",
    "sourceMap": "/tmp/ejfkdev/dj/example.com/source_map",
    "html": "/tmp/ejfkdev/dj/example.com/html/web.html"
  }
}

Caching

Caching is enabled by default. Cache is stored in the system temp directory:

OS	Cache directory
Linux/Mac	/tmp/ejfkdev/dj/
Windows	%TEMP%\ejfkdev\dj\

Cache structure:

<temp_dir>/ejfkdev/dj/<origin>/
├── js/                    # Downloaded JS files
├── source_map/            # Source Map files
├── html/                  # Original HTML
└── meta.json             # Site metadata

FAQ

Why aren't some dynamically loaded JS files being extracted?

This tool uses static analysis of JS code to detect dynamic loading patterns. If a website uses special loading methods, they may not be covered. If you find a website whose dynamic JS cannot be extracted, feel free to submit an Issue with the site URL and any relevant code clues.

License

MPL 2.0 (Mozilla Public License)