@dunx/transform

Load-time transform that lets the dunx container use constructor injection.

export class UsersService {
  constructor(private readonly repo: UsersRepository) {}
}

No @Injectable, no @Inject, no reflect-metadata, no experimentalDecorators. The Providers guide is canonical.

Install

bun add @dunx/transform

Setup

# bunfig.toml
preload = ["@dunx/transform/preload"]

[test]
preload = ["@dunx/transform/preload"]

Or with no config file at all:

bun --preload @dunx/transform/preload src/main.ts

For a production build, pass the plugin to Bun.build:

import { depsPlugin } from '@dunx/transform';

await Bun.build({ entrypoints: ['src/main.ts'], plugins: [depsPlugin] });

Publishing a package

The preload skips node_modules, so a package on npm has to carry its own records or nothing can inject its classes. @dunx/transform/build does that build, reading entrypoints from your exports and bin:

// build.ts
import { buildPackage } from '@dunx/transform/build';

await buildPackage();

It assumes sources under src/, output to dist/, and one tsconfig.json at the package root. Declarations come from typescript, an optional peer, because Bun emits none. The full walkthrough is in the publishing guide.

What it does

It parses each file with oxc-parser and reads every class declaration's constructor parameter types. Then it appends one statement per class:

Object.defineProperty(UsersService, Symbol.for('dunx.deps'), {
  value: () => [UsersRepository],
});

@dunx/core reads that record and resolves the arguments before calling new.

The record is a thunk, a function that returns the parameter types. The container calls it when it resolves the class, not when the file loads. So a dependency declared later in the file, or reached through a circular import, needs no forwardRef.

Only the appended statement is added. Every other byte of the original source is preserved, so comments, formatting, and the line numbers in stack traces are unchanged.

Parameters it will not guess

A parameter whose type names nothing that exists at runtime is recorded as unresolved, together with its original source text. The container then throws at boot:

UsersService cannot be constructed: parameter 2 (private readonly cfg: AppConfig)
names nothing that exists at runtime, so there is no token to resolve. Replace
the type with an abstract class, or bind it with token() and read it with
inject(TOKEN) in a field initializer.

This error covers a type-only import, an inline type specifier, a local interface or type alias, a class type parameter, a primitive and a union. For a type-only import, the error tells you to use a value import instead. For the rest, use an abstract class or a token(). A token has no type to put on a parameter, so read it with inject(TOKEN) in a field initializer.

Class expressions are skipped: const X = class Inner {} binds Inner only inside the class body, so a statement appended after it could not reference the name.

If you forget to register it

The container checks ctor.length against the recorded dependencies, so a class the plugin never saw is a boot error rather than a set of undefined fields:

UsersController declares 1 constructor parameter(s) but no dependencies were
recorded for it, so @dunx/transform did not transform UsersController.