Class: Middleware<MiddlewareFn>

The Middleware class implements the chain of responsibility design pattern and allows executing handlers in series.

The middleware handlers can be represented as any value you wish, such as:

• A function: middleware.add(function () { console.log('called') })
• An object with a handle method: middleware.add({ name: 'auth', handle: authenticate })

Example

const context = {};
type MiddlewareFn = (ctx: typeof context, next: NextFn) => void | Promise<void>;

const middleware = new Middleware<MiddlewareFn>();

middleware.add((ctx, next) => {
  console.log("executing middleware");
  await next();
});

await middleware.runner().run((fn, next) => fn(context, next));

Type Parameters

Type Parameter	Description
MiddlewareFn extends any	The type of the middleware function/handler

Constructors

Constructor

new Middleware<MiddlewareFn>(): Middleware<MiddlewareFn>;

Returns

Middleware<MiddlewareFn>

Methods

add()

add(handler: MiddlewareFn): this;

Registers a new middleware handler to the pipeline.

Adding the same middleware handler multiple times will result in a no-op, as handlers are stored in a Set to prevent duplicates.

Parameters

Parameter	Type	Description
handler	MiddlewareFn	The middleware handler to register

Returns

this

The Middleware instance for method chaining

Throws

If the middleware stack is frozen

---

all()

all(): Set<MiddlewareFn>;

Returns all registered middleware handlers.

Returns

Set<MiddlewareFn>

A Set containing all registered middleware handlers

---

clear()

clear(): void;

Removes all registered middleware handlers from the pipeline.

Returns

void

Throws

If the middleware stack is frozen

---

freeze()

freeze(): void;

Freezes the middleware stack to prevent further modifications.

Once frozen, the middleware array is cached and no new handlers can be added, removed, or modified. This method is automatically called when creating a runner.

Returns

void

---

has()

has(handler: MiddlewareFn): boolean;

Checks if a specific handler has already been registered as middleware.

Parameters

Parameter	Type	Description
handler	MiddlewareFn	The middleware handler to check for

Returns

boolean

true if the handler is registered, false otherwise

---

merge()

merge(hooks: Middleware<MiddlewareFn>): void;

Merges middleware handlers from another Middleware instance.

The middleware from the source instance are appended to the current instance.

Parameters

Parameter	Type	Description
hooks	Middleware<MiddlewareFn>	The source Middleware instance to merge from

Returns

void

Throws

If the middleware stack is frozen

---

remove()

remove(handler: MiddlewareFn): boolean;

Removes a specific middleware handler from the pipeline.

Parameters

Parameter	Type	Description
handler	MiddlewareFn	The middleware handler to remove

Returns

boolean

true if the handler was removed, false if it was not found

Throws

If the middleware stack is frozen

---

runner()

runner(): Runner<MiddlewareFn>;

Creates and returns a Runner instance to execute the middleware pipeline.

This method automatically freezes the middleware stack to prevent modifications during execution.

Returns

Runner<MiddlewareFn>

A new Runner instance configured with the current middleware handlers