JsDuck: A Beginner’s Guide to JavaScript DocumentationDocumentation is the bridge between code and people: other developers, future-you, and users who rely on clear, searchable API references. JsDuck is an open-source documentation tool originally developed at Yahoo! specifically for JavaScript projects. It extracts structured documentation from specially formatted comments in your source code and turns them into a navigable, searchable website. This guide walks you through what JsDuck is, why you might use it, how to set it up, and best practices for writing maintainable JavaScript docs.
What is JsDuck?
JsDuck is a documentation generator for JavaScript that parses specially formatted comments and produces static HTML documentation. It follows a Javadoc-like style for comments and supports annotations for classes, methods, properties, examples, and more. Unlike plain README files or ad-hoc docs, JsDuck encourages documentation that lives alongside code, which makes it easier to keep docs accurate and up to date.
Key features:
- Parsers for annotated JavaScript comments
- Output as a searchable, static website
- Support for class, mixin, namespace, method, property, and event annotations
- Example blocks and cross-references
- Configuration options for project layout and output
Why use JsDuck?
- Keeps documentation close to code so it is easier to maintain and less likely to become stale.
- Produces consistent and professional-looking API reference sites.
- Searchable output helps consumers quickly find classes, methods, or properties.
- Useful for libraries and frameworks where an API reference is the primary documentation need.
If your project is library-like (exposing classes, methods, and events) and you want a focused API reference rather than tutorial-style docs, JsDuck is a good fit.
Installing JsDuck
JsDuck is distributed via Ruby gems and runs on Ruby, using a command-line tool to parse source and emit HTML.
Prerequisites:
- Ruby (commonly 2.5+; check current compatibility if using a modern environment)
- A working shell (macOS, Linux, or Windows with WSL or similar)
Install JsDuck:
gem install jsduck If you need to keep gem installs local or avoid system gems, use Bundler and a Gemfile:
# Gemfile source 'https://rubygems.org' gem 'jsduck' Then:
bundle install bundle exec jsduck <options> Comment format and core annotations
JsDuck reads comments placed before the code element they document. Comments are written in a block format beginning with /** and using annotations prefixed by @.
Minimal example:
/** * Represents a point in 2D space. * * @class Point * @constructor * @param {Number} x The x coordinate. * @param {Number} y The y coordinate. */ function Point(x, y) { this.x = x; this.y = y; } Common annotations:
- @class — declares a class or constructor function
- @constructor — indicates the function is intended as a constructor
- @method — documents a method (often inferred)
- @param {Type} name description — documents parameters
- @return {Type} description — documents return values
- @property {Type} name description — documents properties
- @static — marks a member as static
- @private / @protected / @public — visibility modifiers (for docs)
- @extends — indicates inheritance
- @mixins — notes mixins applied to a class
- @example — provides an example code block
- @deprecated — marks items that are no longer recommended
Examples should be indented in the comment or enclosed in a fenced code block for clarity:
/** * Adds two numbers. * * @method add * @param {Number} a * @param {Number} b * @return {Number} * @example * var sum = Calculator.add(2, 3); */ function add(a, b) { return a + b; } Generating documentation
Basic command:
jsduck path/to/src -o path/to/output Common options:
- -o, –output DIR — output directory for the generated site
- –title TITLE — title of the generated documentation
- –project-version VERSION — set project version shown in docs
- –builtin CSS/JS — include custom assets (themes or styles)
- –config FILE — load configuration from a JSON file
A simple workflow:
- Annotate your source files.
- Run jsduck with the source directory and an output folder.
- Open index.html in the output folder to view the doc site.
For CI/CD, add a script step that runs JsDuck and deploys the generated HTML to your static hosting (GitHub Pages, Netlify, S3, etc.).
Organizing your code for better docs
- Keep public API in dedicated files or a single entry point when possible — makes it easier for JsDuck to find and document exported symbols.
- Use namespaces (via @namespace) to group related classes and functions.
- Use @private for internal helpers you don’t want surfaced in public docs.
- Provide examples for non-trivial classes and methods — examples are often the most valuable part of API docs.
Example using namespace and class:
/** * Utilities for geometry operations. * @namespace geometry */ /** * Calculates the area of a rectangle. * * @class Rectangle * @constructor * @param {Number} width * @param {Number} height */ function Rectangle(width, height) { this.width = width; this.height = height; } /** * Get the area. * @method area * @return {Number} */ Rectangle.prototype.area = function() { return this.width * this.height; }; Examples, code snippets and runnable demos
- Use @example blocks for small snippets demonstrating usage.
- For larger examples, link to external example files and include them in the docs build.
- Keep examples concise and realistic — they should show typical usage patterns.
Styling and theming
JsDuck includes a default theme that produces a clean API reference. You can customize by providing your own CSS and JavaScript. Use the –builtin flag or place assets in expected folders in the output and configure templates if needed. For full branding, replace header/footer templates and include your project logo.
Tips and best practices
- Write comments as if explaining to a competent newcomer: concise, example-driven, and focused on how to use an API rather than implementation details.
- Keep comments near the code they document; when refactoring, update comments immediately.
- Favor examples that show real use cases.
- Mark internal functions @private so they don’t clutter public docs.
- Run JsDuck as part of your build to catch missing or malformed annotations early.
- Use consistent terminology and formatting in descriptions.
Migrating from JSDoc or other tools
JsDuck is similar in spirit to JSDoc but has different annotations and output. If migrating:
- Inventory existing JSDoc comments.
- Map JSDoc tags to JsDuck equivalents (many are identical: @param, @return, @example).
- Test with a subset of files and iterate until output looks correct.
- Consider whether existing templates/themes can be reused or need adaptation.
Limitations and considerations
- JsDuck is focused on API reference generation, not tutorial-style documentation or rich guides (pair it with a docs site generator for that).
- Check compatibility with modern JS syntax or transpile (Babel) if JsDuck’s parser doesn’t handle certain newer constructs.
- The project activity level can vary—confirm it fits your long-term maintenance expectations or be prepared to fork/customize.
Quick checklist to get started
- [ ] Install Ruby and gem install jsduck (or add to Bundler)
- [ ] Add JsDuck-formatted comments to public API items
- [ ] Run jsduck src -o docs
- [ ] Review docs, add examples and tweak visibility tags
- [ ] Automate doc generation in CI and deploy to static hosting
JsDuck provides a practical way to create maintainable, searchable API documentation that lives with your code. For library authors who need a straightforward reference site and prefer documentation embedded in source files, JsDuck remains a useful option.
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