Javascript recursively get all transferables from object

get_transferables.js

// This is also a demonstration of the Z-combinator.
// h/t https://thenewobjective.com/types-and-programming-languages/deriving-the-z-combinator
const Z = (f => (u => f((...x) => u(u)(...x)))(u => f((...x) => u(u)(...x))));


/* Example usage:
a = new MessageChannel().port1;
b = new ArrayBuffer(42);
my_obj = {a, x: {b, a_again: a}}
get_transferables(my_obj);
*/

var get_transferables = Z(f => (
	obj,
	t=(Object.assign(
		(
			[	/* https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Transferable_objects#supported_objects */
				'ArrayBuffer',
				'MessagePort',
				'ReadableStream',
				'WritableStream',
				'TransformStream',
				'WebTransportReceiveStream',
				'WebTransportSendStream',
				'AudioData',
				'ImageBitmap',
				'VideoFrame',
				'OffscreenCanvas',
				'RTCDataChannel',
			]
			.map((()=>{
				"use strict";
				if (!(this))
					throw new InternalError();
				return (clsName => this[clsName]);
			})())
			.filter(cls => cls)
		),
		{
			[Symbol.hasInstance](obj) {
				return this.some(cls => obj instanceof cls);
			}
		}
	)),
	acc=null
) => {
	acc = acc || new WeakSet();

	if (typeof obj !== 'object') {
		// 1. Dead Leaf
		return [];

	} else if (obj instanceof t) {
		// 2. Transferable Leaf
		if (!acc.has(obj))
			// 2a. New Leaf
			return [obj, ...f(obj, t, acc.add(obj))];
		else
			// 2a. Duplicate or ignored Leaf
			return [];

	} else {
		// 3. Branch
		return Object.entries(obj).flatMap(
			([,obj_]) => f(obj_, t, acc) // FIXME this requires mutation of acc
		); 

	}
});