duplexify-tests.ts

import Duplexify = require("duplexify");

new Duplexify();
new Duplexify(writable);
new Duplexify(undefined, readable);
new Duplexify(undefined, undefined, opts);
new Duplexify(writable, readable);
new Duplexify(undefined, readable, opts);
new Duplexify(writable, undefined, opts);
new Duplexify(writable, readable, opts);

declare class _MyStream {
  setPipeline(): void;
}
// you cannot use `extends Duplexify` above because there will be an error regarding
// the static side of the definition not matching. but you can use the following statement
// to get a value and type that extends Duplexify
const MyStream = _MyStream as (typeof _MyStream & typeof Duplexify);

const s = new MyStream();
s.end();
_MyStream.setPipeline(); // <- this is still an error!

index.d.ts

/// <reference types="node" />

import { Writable, Readable, Duplex, DuplexOptions } from 'stream';

declare class _Duplexify extends Duplex {
    constructor(writable?: Writable, readable?: Readable, opts?: DuplexOptions);
    setWritable(writable: Writable): void;
    setReadable(readable: Readable): void;
}

type Duplexify = _Duplexify

interface DuplexifyFactory {
    (writable?: Writable, readable?: Readable, opts?: DuplexOptions): Duplexify;
}

declare const Duplexify: typeof _Duplexify & DuplexifyFactory;

export = Duplexify