Orientation
Content Processing
Search Infrastructure
Rendering and UI
Developer Tooling
How It Works
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The Story Visualizer is a sophisticated documentation subsystem designed to bridge the gap between static component documentation and interactive development environments. Its primary purpose is to automatically extract type information from TypeScript components at build time (or runtime, via caching) and generate an interactive control interface for those components within documentation pages.
By leveraging ts-morph to analyze static types, the Story Visualizer eliminates the manual overhead of writing and maintaining complex component props tables or playground controls. It generates a "Type Tree"—a structural representation of component props—which is then consumed by the client-side WithControl component to render an interactive editor. This system is architected for maximum automation, ensuring that changes to component interfaces are reflected in the documentation immediately upon build.
The architecture centers around a high-precision type-to-node transformation pipeline. It handles complex TypeScript features such as unions, intersections, literal types, and object properties by recursively walking the type graph and converting it into a JSON-serializable TypeNode format. This serialization enables the subsystem to work across various environments, from standard build-time environments (Vite/Webpack) to restricted serverless environments where full compiler access might be prohibited.
The core mechanism for generating story controls is the TypeTreeBuilder. This system uses a modular handler pattern to convert ts-morph Type objects into a custom TypeNode schema. The builder walks the type graph, applying specific handlers for primitive types, enums, arrays, and complex objects.
The traversal is governed by a prioritized sequence of handlers. If a handler cannot process a type, it delegates to the next handler.
Sources: packages/story/src/type-tree/builder.ts:233-282
Note
The cache is implemented using Map<TypeToNodeFlag, WeakMap<Type, TypeNode>> to prevent memory leaks while ensuring deterministic performance when processing deep type trees. The WeakMap uses the Type object itself as a key, ensuring that nodes are garbage collected when the compiler project is disposed.
The transformStoryFile utility performs the "magic" of story generation at build time. It intercepts files matching the story pattern, scans for defineStory function calls, and generates the necessary metadata.
findDefineStoryCalls identifies all defineStory invocations.generateControls creates a temporary type alias in the source file, which acts as a bridge to obtain the component's props type.TypeNode tree is serialized into a JSON string and injected back into the source file as an _generated property.Sources: packages/story/src/utils/transform.ts:25-45
Once a story is loaded in the browser, the WithControl component provides the interactive UI. It uses the stf (Story State Framework) to manage the state of component properties.
The key design choice here is the use of useDeferredValue for argument updates. This ensures that the documentation interface remains responsive even if the component being visualized is computationally expensive or prone to re-rendering.
Sources: packages/story/src/client/with-control.tsx:28-81
The TypeNode is the foundational structure for story controls. It is a discriminated union that allows the WithControl component to dynamically render the appropriate input field for any given property type.
Sources: packages/story/src/type-tree/types.ts
The Story Visualizer employs strict guards during the traversal of type definitions to avoid infinite recursions or unhandled edge cases.
Warning
TypeToNodeFlag.NoIntersection is a critical flag used to prevent the builder from descending infinitely into recursive intersections. When set, it forces the parser to treat the intersection as a terminal node.
Important
The collapse function performs a deterministic state reduction. It should be used when fixed values are provided by the user. If an object property is provided as a fixed value, it recursively prunes the TypeNode tree to remove irrelevant properties, optimizing the rendering process.
Sources: packages/story/src/type-tree/builder.ts:5-8, 284-317
Developers can define a story with custom controls or use the default generated ones.
import { defineStoryFactory } from '@fumadocs/story';
import { Button } from './components/button';
const { defineStory } = defineStoryFactory();
export const MyStory = defineStory('/path/to/component.tsx', {
Component: Button,
args: {
initial: { variant:
Sources: packages/story/src/index.tsx:105-157
Batching updates via setTimeout to limit re-renders |
enum | Select dropdown | members (label, value) |
object | FieldSet grouping | properties (name, type, required) |
union | Polymorphic controls | types (array of TypeNode) |