Deno and Bun — two other runtimes, and what differs

Level: 201 · for readers who use Node and have heard of Deno or Bun

Stub — an outline, not a lesson. There is no runnable example behind this page yet, so nothing on it has been through the check that backs every other claim in this library. The questions below are what the finished page has to answer.

One line: Deno, Bun and Node run the same language on different hosts: Deno refuses file, network and environment access until a flag grants it, a model Node offers only under --permission; and all three run a .ts file by dropping its types, not checking them.

Keywords: Deno, Bun, --permission, --allow-read

What the finished page will answer

• What does reading /etc/hosts do under plain node, under node --permission, and with --allow-fs-read=/etc/hosts?
• Which flags does Deno need for a script that reads a file, calls fetch and reads an environment variable?
• What do node file.ts, deno run file.ts and bun file.ts do with a type error, and what do tsc --noEmit and deno check do?
• Which of node:fs, Deno.readTextFile and Bun.file runs in the other two runtimes?
• How do node --test, deno test and bun test differ in which files they find and whether they type-check?

Examples it will need

• deno_and_bun_node_permission_sh.sh — reading /etc/hosts under plain node, under --permission (ERR_ACCESS_DENIED) and with --allow-fs-read
• deno_and_bun_same_script_sh.sh — one script's output under node, deno and bun where each is installed, with its version, and a skip line where not

See also

• The language and the host — the language is shared; the host differs
• Running TypeScript — the way Node itself runs .ts
• The built-in test runner — node --test, beside deno test and bun test
• Which features your Node has — checking a runtime before relying on a feature

Sources to start from

• Deno — Security and permissions ↗
• Bun — Runtime ↗
• Node.js 24 — Permission Model ↗