Deno 1.36

Deno 1.36: More flexible security and expanded testing APIs

At the core of Deno’s design goals is flexible and robust runtime security. With Deno 1.36, we’re expanding your security options even further with --deny-* flags. Along with our existing --allow-* flags, you can now configure both allow and deny lists for network communication, file system access, and other potentially sensitive APIs.

Along with these security features, you’ll find improved testing and benchmarking APIs, more robust Node.js and npm package support, language server improvements, and much more in 1.36.

If you have Deno installed, you can upgrade to version 1.36 in your terminal with:

deno upgrade

Read on to learn more about the latest features and fixes available in Deno 1.36!

Deno 1.36 at a glance

More flexible security options for Deno programs

The Deno runtime offers security by default, empowering developers to opt in to letting their code and dependencies make network requests, access the filesystem, or use other potentially hazardous APIs with the --allow-* CLI flags.

These options are and remain useful, but they are a bit inflexible in certain scenarios. You can either give your program unfettered access to a given feature, or you would have to configure specific domains or directories the --allow-* options would enable. There’s no way to open up the sandbox with just some domains or file paths excluded. In Deno 1.36, we introduce the --deny-* family of runtime flags to enable more flexible permissions for your Deno programs.

For example, if you’d like your program to have access to any URL it would like, except for a few specific IP addresses and domains, you can use:

$ deno run --allow-net mod.ts

For instance, if you want to give your program access to the whole filesystem, except the /etc directory:

$ deno run --allow-read --deny-read=/etc --allow-write --deny-write=/etc mod.ts

Every CLI flag that previously had an --allow-* option will now have corresponding --deny-* options too. The deny flags have higher precedence than the allow flags, so if you use both on the same domains or a file path, the access will still be denied:

$ deno run --allow-read=foo.txt --deny-read=foo.txt mod.ts
error: PermissionDenied: Requires read access to "foo.txt"...

A special shoutout is called for here to Asher Gomez and Nayeem Rahman, who led the implementation of this new feature. Thanks a ton for your contributions!

We intend to further improve and expand the capabilities of the permission system in the future. One of the features we are looking to implement is the ability to use pre-defined permissions from a configuration file - follow this issue for updates.

We’d love to hear your feedback on the new --deny-* flags, and about any other needs you have related to the permission system. Let us know in Discord, during one of our live events (also found on the Discord), or by raising an issue in GitHub.

Expanded options for testing and benchmarking

Deno 1.36 also introduces improvements to testing and benchmarking in your applications. On the testing side, you can now output the results of deno test runs using new, custom formatters.

JUnit reporter

Having a machine-readable test report is crucial in automated QA of your tests and keeping large codebases maintainable. The JUnit XML format can be consumed natively by many services like GitLab, CircleCI, Jenkins or BuildPulse. Starting with Deno 1.36, you can pass the --reporter=junit flag to deno test to get structured report data:

# Print a JUnit report to the terminal so you can process it further…
$ deno test --reporter=junit

# …or write it directly to a file alongside the default human-readable output.
 deno test --junit-path=test_report.xml

Dot reporter

For folks who prefer short and sweet test reports we added a dot reporter that provides a concise output, removing a lot of noise.

deno test --reporter=dot

node:test polyfill

If you are coming to Deno from recent releases of Node.js, you can now use the built-in test API from Node 20 in addition to Deno.test or describe/it API from the standard library.

Check it out for yourself in Deno with a simple test harness like the one below.

import assert from "node:assert";
import test from "node:test";

test("synchronous passing test", (t) => {
  // This test passes because it does not throw an exception.
  assert.strictEqual(1, 1);

test("asynchronous passing test", async (t) => {
  // This test passes because the Promise returned by the async
  // function is not rejected.
  assert.strictEqual(1, 1);

Not all API surface area has been covered yet, so if you hit a problem we would greatly appreciate a bug report.

deno bench improvements

The granularity and precision of benchmarking in Deno have been improved with the addition of new functionality to Deno.bench.

In previous releases of Deno, the Deno.bench function gave surprising results for the first bench case run due to a phenomenon called “JIT bias” - the V8 engine was over-optimizing benchmarked function and then bailing out of the optimization on the subsequent functions, leading to non-representative results. This has now been fixed, by running a “warmup” function before user defined bench cases.

Additionally, you can now use Deno.BenchContext.start and Deno.BenchContext.end to tell the benchmarking tool about the critical section you want to measure. Everything outside of the section between these two calls will be excluded from the measurement.

import { readAll } from "";

Deno.bench("foo", async (b) => {
  // Open a file that we will act upon.
  const file = await"a_big_data_file.txt");

  // Tell the benchmarking tool that this is the only section you want
  // to measure.

  // Now let's measure how long it takes to read all of the data from the file.
  await readAll(file);

  // End measurement here.

  // Now we can perform some potentially time-consuming teardown that will not
  // taint out benchmark results.

We also updated deno bench output to include information about iterations per second:

Output from deno bench showing iter/s column

Node.js compatibility improvements

Run scripts from npm that aren’t configured as binaries

You can now run scripts from npm packages that are not configured in a package’s bin property in package.json. Example:

deno run -A npm:somepackage@0.0.1/foo/cli.mjs

process.dlopen is available

You can now use process.dlopen API to load native addons for Node.js.

AsyncLocalStorage up to 3.5x faster

We optimized the implementation of AsyncLocalStorage from node:async_hooks module. Our benchmarks show that it’s up to 3.5x faster than in Deno v1.35.3.

node:os is fully polyfilled

The getPriority, setPriority, and userInfo functions of the Node.js os module are now available, making node:os module fully pollyfilled.

Learn more about using Node.js built-ins in the Deno Manual.


import { getPriority } from "node:os";


Quality of life improvements

Below, we’ve included a few other features and bug fixes that made their way into the release that we think will make a meaningful impact in your day-to-day work.

deno compile --no-terminal

A new --no-terminal flag can now be used with deno compile. If the compiled binary is run on Windows, this flag will prevent the terminal window from being opened.


The unstable Deno.createHttpClient now supports the allowHost option, making it possible to specify a Host header for a fetch request.

const client = Deno.createHttpClient({
  allowHost: true,
const res = await fetch("", {
  headers: {
    "host": "",

Allow HTTP(S) URLs in WebSocket API

You can now use http: and https: URLs in the WebSocket Web API, Deno will automatically adjust the protocol to use ws: or wss: respectively:

const url = new URL("");
const ws = new WebSocket(url);
// wss://

Retry failed module downloads

Deno is now more resilient when downloading dependencies. Connecting to remote hosts can always fail due to intermittent connection problems or spurious errors on the remote server.

On such occasions, Deno will wait a short amount of time and retry the download, making CI pipelines more reliable and reducing the need to re-run commands.

More helpful errors in Deno.Command API

Before 1.36, if you tried to spawn a subprocess for a binary that was non-existent with Deno.Command, you were presented with an unhelpful error message:

$ deno
> new Deno.Command("this-binary-does-not-exist").spawn();
Uncaught NotFound: No such file or directory (os error 2)
    at spawnChildInner (ext:runtime/40_process.js:162:17)
    at spawnChild (ext:runtime/40_process.js:182:10)
    at Command.spawn (ext:runtime/40_process.js:440:12)
    at <anonymous>:2:48

With Deno 1.36, the error message will include the name of the binary that was not found:

$ deno
> new Deno.Command("this-binary-does-not-exist").spawn();
Uncaught NotFound: Failed to spawn: this-binary-does-not-exist: No such file or directory (os error 2)
    at spawnChildInner (ext:runtime/40_process.js:162:17)
    at spawnChild (ext:runtime/40_process.js:182:10)
    at Command.spawn (ext:runtime/40_process.js:440:12)
    at <anonymous>:2:48

LSP improvements

Deno 1.36 contains a plethora of fixes and improvements to the LSP. This should make using Deno with an editor that supports an LSP (like Visual Studio Code) significantly more pleasant. Here are a few of the changes:

Still want to learn more?

Believe it or not, the changes listed above still don’t tell you everything that got better in 1.36. You can view the full list of pull requests merged in Deno 1.36 on GitHub here.

Thank you to our community contributors!

We couldn’t build Deno without the help of our community! Whether by answering questions in our community Discord server or reporting bugs, we are incredibly grateful for your support. In particular, we’d like to thank the following people for their contributions to Deno 1.36.

Would you like to join the ranks of Deno community contributors? Check out our contribution docs here, and we’ll see you on the list next time.

Thank you for catching up with our 1.36 release, and we hope you love building with Deno!

🍋 Did you know? Fresh just got fresher.

Be sure to check out the release notes for Fresh 1.3, the latest iteration of the next-gen web framework for Deno.