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Deno 1.8 Release Notes

March 2nd, 2021
Bartek IwaƄczuk, Luca Casonato, Ryan Dahl

Today we are releasing Deno 1.8.0. This release contains a massive amount of new features and stabilizations:

If you already have Deno installed you can upgrade to 1.8 by running deno upgrade. If you are installing Deno for the first time, you can use one of the methods listed below:

# Using Shell (macOS and Linux):
curl -fsSL | sh

# Using PowerShell (Windows):
iwr -useb | iex

# Using Homebrew (macOS):
brew install deno

# Using Scoop (Windows):
scoop install deno

# Using Chocolatey (Windows):
choco install deno

New features and changes

Experimental support for the WebGPU API

The WebGPU API gives developers a low level, high performance, cross architecture way to program GPU hardware from JavaScript. It is the effective successor to WebGL on the Web. The spec has not yet been finalized, but support is currently being added to Firefox, Chromium, and Safari; and now also in Deno.

This API gives you access to GPU rendering and general purpose GPU compute right from within Deno. Once finished, stabilized, and unflagged, this will provide a portable way to access GPU resources from web, server, and developer machine.

GPUs allow programmers to make some numerical algorithms highly parallel. This is useful beyond rendering graphics and games. Effective use of GPUs in Machine Learning has enabled more complex neural networks - what is called Deep Learning. The rapid progress in computer vision, translation, image generation, re-enforcement learning, and more all stem from making effective use of GPU hardware.

These days, most neural networks are defined in Python with the computation offloaded to GPUs. We believe JavaScript, instead of Python, could act as an ideal language for expressing mathematical ideas if the proper infrastructure existed. Providing WebGPU support out-of-the-box in Deno is a step in this direction. Our goal is to run Tensorflow.js on Deno, with GPU acceleration. We expect this to be achieved in the coming weeks or months.

Here is a basic example that demonstrates accessing an attached GPU device, and reading out the name and supported features:

// Run with `deno run --unstable`

// Try to get an adapter from the user agent.
const adapter = await navigator.gpu.requestAdapter();
if (adapter) {
  // Print out some basic details about the adapter.
  console.log(`Found adapter: ${}`);
  const features = [...adapter.features.values()];
  console.log(`Supported features: ${features.join(", ")}`);
} else {
  console.error("No adapter found");

Here is a little example that demonstrates the GPU rendering a simple red triangle on a green background using a render shader:

$ deno run --unstable --allow-write=output.png

A simple red triangle on a green background

Note the use of WebAssembly to write the PNG. For more examples visit this repository:

The final PR weighed in at a whopping 15.5k lines of code, and took a whole 5 months to merge after opening. Many thanks to crowlKats who led the integration of WebGPU into Deno. We would also like to thank to all contributors to the wgpu and gfx-rs projects that underpin the WebGPU implementation in Deno. Special thanks also to kvark, editor on the WebGPU spec, and the lead developer of wgpu and gfx-rs, for the great guidance while implementing the WebGPU API.

ICU support

ICU support has been the second most requested feature in Deno repository. We're happy to announce that Deno v1.8 ships with full ICU support.

All JavaScript APIs depending on ICU should now match browser APIs.

Try it in the REPL:

$ deno
Deno 1.8.0
exit using ctrl+d or close()
> const d = new Date(Date.UTC(2020, 5, 26, 7, 0, 0));
> d.toLocaleString("de-DE", {
	weekday: "long",
	year: "numeric",
	month: "long",
	day: "numeric",
"Freitag, 26. Juni 2020"

Revamped coverage tooling: deno coverage

This release expands our coverage infrastructure to add some great new capabilities. The main change in this release is that coverage handling is now split into coverage collection and coverage reporting.

Previously coverage collection and reporting would all happen in a single subcommand, by specifying the --coverage flag when starting deno test. Now the --coverage flag for deno test takes an argument - a path to a directory where to store the collected profiles. This is the coverage collection. In a second step you now call deno coverage with the path to the directory storing the coverage profiles. This subcommand can either return a report as pretty text output right on the console, or it can output an lcov file (--lcov flag) for use with tools like genhtml,, or

We have been dogfooding this feature on deno_std for a few days now. We upload a coverage report to for each commit. You can view these here Adding this was trivial, with only a 10 line change to our GitHub Actions workflow:

- name: Run tests
-        run: deno test --unstable --allow-all
+        run: deno test --coverage=./cov --unstable --allow-all
+      - name: Generate lcov
+        run: deno coverage --unstable --lcov ./cov > cov.lcov
+      - name: Upload coverage
+        uses: codecov/[email protected]
+        with:
+          name: ${{ matrix.os }}-${{ matrix.deno }}
+          files: cov.lcov

For an example of integration with, see this repository:

Import maps are now stable

Import maps were stabilized in Chrome 89, and following that our implementation has been updated to match the latest revision of the specification and is now also considered stable. This means that the --unstable flag is no longer required when using --import-map.

$ deno run --import-map=./import_map.json ./mod.ts

Additionally the --import-map flag now accepts not only local paths, but also URLs, allowing you to load import maps from remote servers.

$ deno run --import-map= ./mod.ts

Import maps allow a user to use so-called "bare" specifiers for dependencies, instead of relative or absolute file / http URLs:

// Deno does not support such specifiers by default,
// but by providing an import map, users can remap bare specifiers
// to some other URLs.
import * as http from "std/http";
  "imports": {
    "std/http": "[email protected]/http/mod.ts"

Users should keep in mind that import maps are not composable: this means you can only provide a single import map to deno run / deno test. Because of this library authors should still use regular, non-bare specifiers (relative or absolute file / http URLs); otherwise the users of the library will manually need to add your libraries (and your libraries dependencies) bare specifiers into their import map.

A much more useful feature for import maps is ability to remap regular specifiers to completely different ones. For example if you have some broken dependency that is deeply nested in your module graph you can replace it with fixed version before it's fixed upstream, or if you use a build process that adds hashes to your modules filenames, you can refer to the file without hashes in your source code and remap the specifiers only at runtime using an import map.

For more examples and a detailed explanation refer to the specification.

Auth token support for fetching modules

Not all code is openly available on the public internet. Previously Deno had no capability to download code from a server that required authentication. In this release we have added the ability for users to specify per domain auth tokens that are used when fetching modules for the first time.

To do this the Deno CLI will look for an environment variable named DENO_AUTH_TOKENS to determine what authentication tokens it should consider using when requesting remote modules. The value of the environment variable is in the format of a n number of tokens delimited by a semi-colon (;) where each token is in the format of {token}@{hostname[:port]}.

For example a single token for would look something like this:

[email protected]

And multiple tokens would look like this:

[email protected];[email protected]:8080

When Deno goes to fetch a remote module, where the hostname matches the hostname of the remote module, Deno will set the Authorization header of the request to the value of Bearer {token}. This allows the remote server to recognize that the request is an authorized request tied to a specific authenticated user, and provide access to the appropriate resources and modules on the server.

For a more detailed usage guide and instructions for configuring your environment to pull from private GitHub repos, see the related manual entry.

Exit sanitizer for Deno.test

The Deno.test API already has two sanitizers that help ensure that your code is not "leaking" ops or resources - ie. that all open file/network handles are closed before test case ends, and that there are no more pending syscalls.

Deno 1.8 adds a new sanitizer that ensures that tested code doesn't call Deno.exit(). Rogue exit statements can signal false positive test results and are most often misused or were forgotten to be removed.

This sanitizer is enabled by default for all tests, but can be disabled by setting the sanitizeExit boolean to false in the test definition.

  name: "false success",
  fn() {
  sanitizeExit: false,

// This test is never run
  name: "failing test",
  fn() {
    throw new Error("this test fails");

You can run this script yourself: deno test

Deno.permissions APIs are now stable

Deno's security model is based on permissions. Currently these permissions can only be granted when the application is started. This works well for most scenarios, but in some cases it is a better user experience to request / revoke permissions at runtime.

In Deno 1.8 there is now a stable API to query, request, and revoke permissions. These APIs are contained in the Deno.permissions object. Here is an example of how this works:

function homedir() {
  try {
    console.log(`Your home dir is: ${Deno.env.get("HOME")}`);
  } catch (err) {
    console.log(`Failed to get the home directory: ${err}`);

// Try to get the home directory (this should fail, as no env permission yet).

const { granted } = await Deno.permissions.request({ name: "env" });
if (granted) {
  console.log(`You have granted the "env" permission.`);
} else {
  console.log(`You have not granted the "env" permission.`);

// Try to get the home directory (this should succeed if the user granted
// permissions above).

await Deno.permissions.revoke({ name: "env" });

// Try to get the home directory (this should fail, as the permission was
// revoked).

You can run this script yourself: deno run

This release brings stabilization four APIs related to symlinks:

Before stabilization these APIs went through a security review and proper permissions are required to use them. and Deno.linkSync require both read and write permissions for both source and target paths.

Deno.symlink and Deno.symlinkSync require write permissions for target path.

More granular Deno.metrics

As Deno becomes more stable it is becoming more important have easy ways for developers to instrument their applications. This starts at the lowest level, at the runtime itself. In Deno all privileged operations in JS (the ones that go to Rust), are done via a single central interface between JS and Rust. We call the requests going over that interface "ops". For example, calling would invoke the op_open_async op to the privileged side, which would return the resource id of the opened file (or an error).

More than two years ago, on Oct 11, 2018 we added a way for you to view metrics for all of the ops between Rust and JS: Deno.metrics. This API currently exposes the count of started, and completed synchronous and asynchronous ops, and the amount of data that has been sent over the ops interface. So far this has been limited to combined data for all of the different ops. There was no way to figure out which ops were invoked how many times, only all ops in general.

When running with --unstable, this release adds a new field to Deno.metrics called ops. This field contains per op information about how often the API was invoked and how much data has been transmitted over it. This allows for far more granular instrumentation of the runtime.

Here is an example of this working:

$ deno --unstable
Deno 1.8.0
exit using ctrl+d or close()
> Deno.metrics().ops["op_open_async"]
> await"./")
File {}
> Deno.metrics().ops["op_open_async"]
  opsDispatched: 1,
  opsDispatchedSync: 0,
  opsDispatchedAsync: 1,
  opsDispatchedAsyncUnref: 0,
  opsCompleted: 1,
  opsCompletedSync: 0,
  opsCompletedAsync: 1,
  opsCompletedAsyncUnref: 0,
  bytesSentControl: 54,
  bytesSentData: 0,
  bytesReceived: 22

In an upcoming release this new information will be used by the async op sanitizer in Deno.test to give more actionable errors when an async op is not completed before test completion. We have already seen this feature being used to instrument applications and pipe the data into monitoring software:

screenshot of a website with a table displaying the output of Deno.metrics

JSON support for deno fmt

deno fmt can now format .json and .jsonc files. Just like with JS/TS, the formatter will also format json and jsonc codeblocks inside of markdown files.

IIFE bundle support for Deno.emit

The built-in bundler can now emit bundles in Immediately Invoked Function Expression (IIFE) format.

By default output format will still be esm, but users can change this by setting the EmitOptions.bundle option to iife:

const { files } = await Deno.emit("/a.ts", {
  bundle: "iife",
  sources: {
    "/a.ts": `import { b } from "./b.ts";
    "/b.ts": `export const b = "b";`,


Results in:

(function() {
    const b = "b";
    return {

You can run this script yourself: deno run --unstable

This is particularly useful for creating bundles for older browsers that do not support ESM.

deno lsp is now stable

We have been working on a replacement for our old editor integration for VS Code, the Deno extension for the last few months. The old extension only worked for VS Code, and the resolved types did not always match the ones in the Deno CLI.

In Deno 1.6 we released deno lsp in canary - a builtin language server for Deno. LSP allows us to provide editor integration to all LSP capable editors from just a single codebase. The built in language server is built on the same architecture as the rest of the Deno CLI - it thus provides TypeScript diagnostics the same way as the rest of the CLI.

Two weeks ago, in Deno 1.7.5 we stabilized deno lsp and switched our offical VS Code extension to use it. So far we have gotten some great feedback, and will be working to address all reported issues. If you are running into issues with the extension, please report it on our issue tracker. We can not fix issues that we do not know about.

In addition to the offical VS Code integration, more community integrations have been created that are built on deno lsp:

TypeScript 4.2

Deno 1.8 ships with the latest stable version of TypeScript.

For more information on new features in Typescript 4.2 see Announcing TypeScript 4.2