🧬 TFusion

_"Understand your types. Flatten the complexity."_

> Flatten any TypeScript type — no matter how deep, generic or entangled — into a clean, inspectable, plain-text structure.

⚡ Example

Your regular types, split across multiple files:

user.ts:

``ts
export type UserProfile = {
name: string;
email: string;
};

export type UserPreferences = {
theme: "light" | "dark";
notifications: NotificationPreferences;
};

type NotificationPreferences = {
enabled: boolean;
};
`

api-response.ts:

`ts
import type { UserPreferences, UserProfile } from "./user";

type ApiResponse = {
data: T;
meta: {
pagination?: {
page: number;
limit: number;
total: number;
};
cache: {
ttl: number;
revalidate: boolean;
};
};
};

type User = {
id: number;
profile: UserProfile;
preferences: UserPreferences;
posts: Post[];
};

type Post = {
id: number;
title: string;
tags: { id: string; name: string }[];
stats?: { views: number; likes: number };
};

export type UserResponse = ApiResponse;
export type PostResponse = ApiResponse;
`

Just pass api-response.ts file to TFusion, it will return an array of ResolvedType objects:

`ts
type UserResponse = {
data: {
id: number;
profile: {
name: string;
email: string
};
preferences: {
theme: ("light" | "dark");
notifications: {
enabled: boolean
}
};
posts: {
id: number;
title: string;
tags: Array<{
id: string;
name: string
}>;
stats?: {
views: number;
likes: number
}
}[]
};
meta: {
pagination?: {
page: number;
limit: number;
total: number
};
cache: {
ttl: number;
revalidate: boolean
}
}
};

type PostResponse = {
data: {
id: number;
title: string;
tags: {
id: string;
name: string
}[];
stats?: {
views: number;
likes: number
}
};
meta: {
pagination?: {
page: number;
limit: number;
total: number
};
cache: {
ttl: number;
revalidate: boolean
}
}
};
`

Check tests folder for more examples.

📦 Install

`bash
[p]npm i -D tfusion


or


yarn add --dev tfusion
`

> Note: tfusion is an ESM-only package and requires Node.js 22 or higher.

🚀 Usage

$3

`ts
import flattener from "tfusion";

const flatDefs = flattener("./path/to/file.ts");
`

This returns an array of ResolvedType objects representing all exported types in the file.
Each flattened literal represents an expanded, serializable version of a TypeScript type — including its parameters, structure, and comments.

`ts
export type ResolvedType = {
kind: keyof typeof SyntaxKind;

/**
* The name of the type, identical to the exported alias in the original file.
/
name: string;

/**
* Type parameters declared on the original type, if any.
*
* Example:
* export type Entry = { ... }
* Will produce:
* [
* { name: "T", text: "T" },
* { name: "R", text: "R = string" }
* ]
/
parameters: Array<{ name: string; text: string; fullText: string }>;

/**
* Any single-line or multi-line comments
* that immediately precede the original type declaration.
/
comments: Array;

/**
* The flattened type body (object literal only), without name or parameters.
/
text: string;

/**
* An array of properties returned for type literals.
* Effective only if withProperties option provided.
/
properties?: Array<{
name: string;
text: string;
optional: boolean;
readonly: boolean;
}>;

};
`

$3

The flattener accepts an optional second argument for customization:

`ts
import flattener from "tfusion";

const flatDefs = flattener("./path/to/file.ts", {
typesFilter: (name) => name.startsWith("API"),
overrides: {
CustomPromise: "Promise",
},
maxDepth: 10,
});
`

`ts
export type UserOptions = {
/**
* by default all exported types will be processed.
* use this filter to only process specific types.
/
typesFilter?: (typeName: string) => boolean;

/**
* a map of types to override default name for.
*
* eg. you have a CustomPromise type that should be rendered as native Promise:
* import { CustomPromise } from "@/lib";
* export type ResponseHandler = () => CustomPromise<...>
*
* then add CustomPromise to overrides:
* overrides: {
* CustomPromise: "Promise",
* }
*
* and the flattened result will be:
* export type ResponseHandler = () => Promise<...>
/
overrides?: Record;

/**
* limit recursion to this level depth.
* @default: 16
/
maxDepth?: number;

/**
* If enabled, removes all comments from the generated output.
* Useful for producing clean, minimal artifacts.
* @default false
/
stripComments?: boolean;

/**
* Controls property resolution behavior for type literals.
* - When true: Resolves properties for ALL type literals encountered
* - When string[]: Resolves properties ONLY for type literals matching the specified names
* - When false: Skips property resolution entirely (default behavior)
/
withProperties?: boolean | Array;

/**
* An array of formatters to apply on resolved types.
/
formatters?: Array;

};
`

$3

If you already have a ts-morph Project and want to reuse it across files:

`ts
import { flattener } from "tfusion";

const flatDefs = flattener(existingProject, "./types/user.ts", options);
`

`ts
// Signature:
(project: Project, file: string | SourceFile, opts?: UserOptions) => ResolvedType[];
`

This is ideal when you're flattening multiple files in one session and want to avoid recreating the project each time.

🔍 Notes

- Performance: This tool prioritizes type correctness over raw speed.

- Reliability: tfusion is thoroughly tested, with over 40 test suites and 1000+ individual tests,
covering most use-cases (but not all; some edge cases are printed as is).

- Disclaimer: TypeScript is complex. Edge cases happen. Contributions and bug reports are welcome.

🧪 Coming Soon

No CLI yet — but one is planned if there's enough interest. Open an issue if that's something you'd use.

🛠 Related

- ts-morph – core engine for AST inspection
- typescript` – the official compiler powering all type resolution