Bartek Iwańczuk bartlomieju

Should Deno Have a Global Config File?

Bun's Global Config

Bun uses bunfig.toml (TOML format) with a two-tier system:

	Local	Global
File	`bunfig.toml` (project root)	`$HOME/.bunfig.toml` or `$XDG_CONFIG_HOME/.bunfig.toml`
Dot prefix	No	Yes

What is a Dev Server?

A dev server is a local HTTP server optimized for the development loop. Its job is to serve your application locally with features that make iteration fast.

Core Features

Hot Module Replacement (HMR) — when you save a file, only the changed module is swapped in the browser without a full page reload. State (like form inputs, scroll position) is preserved.
On-demand transformation — instead of bundling everything upfront, modules are transformed (TypeScript → JS, JSX → JS, etc.) only when the browser requests them. This makes startup near-instant even for large projects.
File watching — monitors the filesystem and triggers rebuilds/HMR updates.
Error overlay — compilation errors are shown directly in the browser.

Issue #26142: Worker blob URL race condition — Analysis & Fix Plan

The Bug

URL.revokeObjectURL() after new Worker(blobURL) causes intermittent "Module not found" errors because blob content is fetched asynchronously on the worker thread, not during construction.

Works in Chrome/Firefox. Fails in Deno.

Race Condition

Fix: node:worker_threads Worker Idle Termination (denoland/deno#23169)

Problem

Workers created with node:worker_threads are terminated when idle, even if they have ref'd transferable objects like MessagePort or SharedArrayBuffer that should keep them alive.

Root Cause: Two Competing Keepalive Systems

There are two independent keepalive decision systems, and that's the root problem:

	# Investigation: Deno Issue #15176 — Resolving Promises in `beforeunload` Event

	## The Problem

	```js
	await new Promise(resolve => {
	window.onbeforeunload = resolve;
	});
	```

	/******/ (() => { // webpackBootstrap
	/******/ "use strict";
	/******/ var __webpack_modules__ = ({

	/***/ "./src/base.ts":
	/!*******************!\
	!* ./src/base.ts *!
	\*********************/
	/***/ (function(__unused_webpack_module, exports, __webpack_require__) {

	❯ cargo run -- task
	Compiling deno v1.19.2 (/Users/ib/dev/deno/cli)
	Finished dev [unoptimized + debuginfo] target(s) in 20.58s
	Running `target/debug/deno task`
	Available tasks:
	- async
	sleep 1 && echo 2 &
	- boolean_list
	echo 1 && false \|\| echo 2
	- env_var_substitution

	addEventListener("fetch", (event) => {
	new ArrayBuffer(1 << 30);
	});

	addEventListener("fetch", (event) => {
	throw new Error("boom!");
	});