From Deno

Deno users will find 3va’s model familiar: everything is denied until you grant it with --allow-* flags. The module system is different, though. 3va follows Node (package.json + node_modules), not Deno’s URL and deno.json imports.

What doesn’t carry over

We ran a Deno 2.9 project unchanged:

import { join } from "@std/path";   // from deno.json "imports"
import ms from "ms";                // "ms": "npm:ms@^2.1.3"

$ 3va run main.ts
Error: Cannot find module '@std/path'

• deno.json / deno.jsonc (imports, tasks, compilerOptions) are not read.
• npm: and jsr: specifiers in source (import ms from "npm:ms@2.1.3") aren’t supported: Cannot find module 'npm:ms@2.1.3'.
• https:// imports aren’t supported.
• The Deno global doesn’t exist: Deno.serve, Deno.readTextFile, Deno.env, Deno.Command all need a Node equivalent.

Step by step

1. Create a package.json with "type": "module".

2. Install each dependency from its registry. 3va picks the registry from --allow-net, so run one command per registry:

   3va install @std/path --allow-net=jsr.io          # JSR
   3va install ms --allow-net=registry.npmjs.org     # npm

   Don’t combine hosts in one command. With --allow-net=jsr.io,registry.npmjs.org, npm packages are looked up on JSR and fail (the install exits with code 1 and doesn’t add them to package.json).

3. Rewrite imports to bare specifiers: "npm:ms@^2.1.3" → "ms", "jsr:@std/path@^1" → "@std/path".

4. Replace Deno.* APIs:

   Deno	3va (Node API)
   Deno.serve(handler)	http.createServer()
   Deno.readTextFile(p)	fs.promises.readFile(p, "utf-8")
   Deno.env.get("X")	process.env.X
   Deno.args	process.argv.slice(2)
   new Deno.Command(cmd)	child_process.spawn(cmd)
   deno task x	package.json scripts
   deno test + @std/assert	3va test + expect

5. Carry your permission flags over. They map almost one to one:

   Deno	3va
   --allow-read, --allow-write, --allow-net, --allow-env	same names
   --allow-run	--allow-child-process
   --allow-ffi	--allow-ffi
   --allow-sys, --allow-hrtime	no equivalent
   -A / --allow-all	no single flag; grant each capability

   One difference: importing local files and packages needs --allow-read in 3va. Deno allows module loading without it.

Things to keep in mind

• JSR packages are installed without their JSR dependencies. @std/path installs, but loading it fails with Cannot find module '@jsr/std__internal/os'. Until that’s fixed, prefer the npm version of a package when one exists.
• Top-level await doesn’t work correctly yet: at module top level it gives you the Promise itself, and a file with no import/export fails to parse. This is very common in Deno code, so wrap such code in an async function main().
• Web APIs are there: fetch, Request/Response, WebSocket, URLPattern, web streams, crypto.randomUUID(), structuredClone, import.meta.dirname and import.meta.main all exist.
• Type-checking: deno check has no counterpart. 3va strips types without checking them, so run tsc --noEmit (on Node) in CI.