forwardRef

Use forwardRef to reference a class that is defined after the class that depends on it.

The Problem

TypeScript/JavaScript evaluates code top-to-bottom. If class A depends on class B, but B is defined after A, the dependency will be undefined:


// ❌ This won't work - Father is undefined when Person is evaluated
class Person {
  constructor(@Inject(Father) readonly father: Father) {}
}
 
class Father extends Person {}

The Solution

Wrap the dependency in forwardRef:


// ✅ This works
class Person {
  constructor(
    @SkipSelf() @Optional(forwardRef(() => Father)) readonly father: Father
  ) {}
}
 
class Father extends Person {
  changeDiaper(): void {}
}

This is a JavaScript/TypeScript behavior, not specific to redi. The same pattern exists in Angular and other DI frameworks.

When to Use

Circular class references
Classes defined after their dependents
Mutual dependencies between files