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Avatar of Tim smiling in a blue polo shirt against a blurred bubble background
Software Engineer specialising in All-Stack™️ Javascript applications for Web, Desktop, Mobile and Electronics

Get stuck in with Tim & Deno

Its not the NodeJS killer, but it might go that way...

Deno? I hear you ask. Deno is a Node(JS) anagram/rival/alternative that is sharply increasing in popularity, particularly after it's 1.0.0 released in May 2020 and aims to be better than its predecessor and fix a lot of its well-known pitfalls.

Table of Contents


  • I'm assuming you're already familiar with Javascript, NPM/Node and have some basic experience using a terminal environment (however, these aren't essential and will be explained briefly as we go).

  • I'll also be assuming you're using a Mac and VSCode (as I am), but I'll try and keep instructions as broad as possible to support as many varied setups as possible.

  • Everything in this article is deemed fit for use with Deno v1.11.1. Given Deno is still relatively young, some parts of this article may no longer be correct and may require updating as and when needed.

What is Deno?

Like Node, Deno is a technology we can use to write "server-side Javascript". In many ways, it is extremely close to Node and I consider it to be a spiritual successor to Node. It shares the same creator and uses the V8 Javascript engine but differs in that it is implemented in Rust rather than C++ and supports both WebAssembly and Typescript by default (no need for a tsconfig.json or any other setup process! However, you can include one for your specific needs).

Deno tries to be as browser-friendly by supporting as many of the current web standard APIs as possible, such as fetch, addEventListener, removeEventListener, setInterval, clearInterval, dispatchEvent and even has a window object that allows us to listen for lifecycle events such as

window.onload = (e) => console.log("Howdy 🤠");

One of the goals of the project was to avoid inventing new APIs, which was a requirement in 2009 by Node for handling operations like requireing modules before the ES6 import/export syntax existed which is why there was a focus on being browser-friendly. However, there are some APIs that it does need to invent for file i/o like Node's top-level FS operations (most of which are available in the standard library). However, Deno differs again as Deno's FS implementation is achieved by a compatibility layer as opposed to writing C++ addons as Node requires)

A common use case I've seen for Deno is combining the pros of its server-side capabilities with ExpressJS for full-stack typescript applications, but the only hands-on experience I've had with it is for building little tools for process automation and document transformations (generating CSVs, automate big copy/paste jobs etc...) but essentially whatever you can do with Node, Deno should be able to do it just as well!

Deno's Standard Library & Third-Party Modules

Deno provides us with a set of standard modules (similar to how NodeJS has built-in modules such as fs, path etc) for common use cases such as serve from the http module via

import { serve } from "";
const server = serve({ hostname: "", port: 8080 });

Note: I'm specifying std@0.92.0 to ensure the correct version is used when others use my project. You can safely omit the version and Deno will grab the latest version instead. In my case, omitting the version gave me the following Warning Implicitly using latest version for

A full list can be found at, along with a more detailed explanation of the Standard library from

If you're looking for third-party modules (such as we'll be using to build a react app later), you'll be able to search for them via in a similar way to using the NPM repository

No more NPM Packages/package.json = No more node_modules

Illustration explaining how the node_modules folder has more gravity than our Sun, a neutron star and black hole

Deno also aims to fix some of the main issues synonymous with its predecessor but can't be altered due to said faults being key to its architecture, hence the need for a clean slate. The elephant in the room being the NPM package dependencies, package.json and the hell they bring with them. Deno does away with all of this extra fat and opts for a much simpler way to import packages by allowing you to include them directly via a URL that a package is being served from. For example, to use an external library for testing we can simply use the ES6 module syntax:

import { assertEquals } from ""; // No need for `npm install`

assertEquals("hello", "hello");
assertEquals("world", "world");

console.log("Asserted! ✓");

The beautify of this is that we don't need to "install" our application, as the packages are only retrieved the first time you run the application which is then cached locally to save requesting them every time a file calls for it - akin to how <script src=""> would work in an HTML document.

Okay, so how do you manage dependencies for big projects?

If your project has a lot of dependencies, it may not make sense to add them to every file they are required in via the absolute URLs. This can be overcome by having a single file (depts.ts by convention) be the home of all the dependencies and export them as needed. For example, here is how the "depts" are managed in our example-react folder:

// example-react/deps.ts

export * as ReactDOM from "";

import * as React from "";

const { default: any, } = React;
const react = React.default;

export { react as React };
export { rest as react };
// example-react/index.tsx

import { React, react, ReactDOM } from "./deps.ts"; // importing react from the depts file
import App from "./App.tsx"; // regular import for our component

    <App />

Note: with Deno support, you may not be able to use them. It can be hit and miss using NPM packages/repos in your project, but one of the things it seems to boil down to in my experience is whether the packages use Node-specific APIs (FS et al), but some may work thanks to Deno's use of compatibility layers and Node polyfills (very experimental).

No more callback hell

All async actions are promised based and having a top-level await means we don't need any extra boilerplate code to resolve our promises!

Improved security measures

Deno is also secure by default. One example would be trying to log the current working directory of the filesystem by using console.log(Deno.cwd()); in your script, then executing deno run index.ts, doing so will give you:

error: Uncaught PermissionDenied: read access to "/path/to/file", run again with the "--allow-read" flag

This means unless you, the developer, run the command and let the script access your filesystem, any requests to do so will result in errors and potentially prevent malicious code from being executed. You can specify more such as allowing write access to the disk, network access, plugin use etc. Here are some examples:

Flag Description
allow-env allow environment access
allow-hrtime allow high-resolution time measurement
allow-net= allow network access
allow-plugin allow loading plugins
allow-read= allow file system read access
allow-run allow running subprocesses
allow-write= allow file system write access
allow-all allow all permissions (same as -A, known as "Node mode")

For a full list of permissions, you can control/specify, see Deno Permissions List


Instructions vary based on OS and how you manage your software/packages. The Deno manual has instructions for most OS's and package managers:

For example, on my Mac, it was as simple as running brew install deno


For setting Deno up for use via shell/cmd and for help setting up your IDE, see

For my setup in VSCode, I just needed to add the VSCode Deno extension and include the following in my .vscode/settings.json:

  "deno.enable": true,

Getting started

Check the install worked

To test your installation and setup are working as intended, let's run the example code by running

deno run welcome.js

and if you see the welcome message, you know everything worked okay 🤠

Example I/O scripts and what they do

Note: Make sure you've CD'd into the example-io folder for these

deno run --allow-read example-read.ts

This file demonstrates how we would use Deno to grab the contents of a text file

This also demonstrates how there is no extra setup for using TS and is supported by default

deno run --allow-read --allow-write example-write.js

This file demonstrates how we would use Deno to write the contents of a text file

Also, note the inclusion of exists imported from the FS in the Deno Standard Library

While Deno.write can overwrite the original file, we're doing this the long way round to demo how to import a Standard Library and use it

deno test

This file demonstrates how we would use Deno to write tests

Also, note the inclusion of imported assert functions from the Deno Standard Library

Example React app

Note: Make sure you've CD'd into the example-react folder to try these out

For demo purposes, we'll be using Deno's version of create-react-app, available to use over at Following the quick start guide from the module's README, we can be up and running as quickly as:

Note The first command uses the unstable flag, which is perfectly safe for our example, but you can find out more here:

# Grab the Third-Party Library for generating create-react-apps
deno install -A --unstable -n deno-create-react-app

# Initialise an instance of a new react app
deno-create-react-app init <name-of-app>

cd <name-of-app>

# Run the project in dev mode
# -w, --watch, watch file change to rebuild, default is true
# -p, --port, server port, default is 8000
deno-create-react-app run -w -p 3000

# Deno also has a built-in linter we can use on our app:
deno lint --unstable --ignore="dist"

# Build the project to dist/build, your app is ready to deploy
deno-create-react-app build

And that's it for the create-react-app 🥳

Example of bundling and compiling to a single executable file

Note: Make sure you've CD'd into the example-compile folder to try these out

Note: Up to now, all examples have been included in the repo but I haven't included the compiled curry-sums due to its large size. Wanna see it? Make your own!

Essentially, deno compile [--output <OUT>] <SRC> creates a self-contained executable file based on your scripts.

In the example folder, you'll see our index.ts requires the add.ts and subtract.ts, which in turn each require the curry.ts. What compile lets us do is produce a single file with all of our required files combined inside of it - our four files become one!

How do we do that? In our case, running this should do it:

# Compile into a single executable
deno compile --unstable --output="compiled-curry-sums" index.ts

# Run the executable we just made

Note Since the compile functionality is relatively new, the --unstable flag has to be set for the command to work.

And if we check inside the output folder we'll find out curry-sums file. To execute it, we can simply run ./output/curry-sums, which should give us the same output as running just the index file (deno run index.ts) - the difference being that our curry-sums file is stand-alone and can be moved anywhere and will still work just fine!

This is great for portability and for protecting the source code when sharing with others, but it does come at a cost... In our case, our file comes to a less than modest 77.80MB (running the compile with the --lite command will use a slimmed-down runtime-only binary, but still creates a ~55MB file)! While NodeJS also has compiling options similar to this, they are producing even bigger outputs than that of Deno (usually 70+MB).

What else can Deno do?

Tim.Bryan@Potato example-deno % deno --help
deno 1.11.1
A secure JavaScript and TypeScript runtime


To start the REPL:


To execute a script:

  deno run

To evaluate code in the shell:

  deno eval "console.log(30933 + 404)"


    -h, --help
            Prints help information

    -L, --log-level <log-level>
            Set log level [possible values: debug, info]

    -q, --quiet
            Suppress diagnostic output
            By default, subcommands print human-readable diagnostic messages to stderr.
            If the flag is set, restrict these messages to errors.
            Enable unstable features and APIs

    -V, --version
            Prints version information

    bundle         Bundle module and dependencies into single file
    cache          Cache the dependencies
    compile        UNSTABLE: Compile the script into a self contained executable
    completions    Generate shell completions
    coverage       Print coverage reports
    doc            Show documentation for a module
    eval           Eval script
    fmt            Format source files
    help           Prints this message or the help of the given subcommand(s)
    info           Show info about cache or info related to source file
    install        Install script as an executable
    lint           Lint source files
    lsp            Start the language server
    repl           Read Eval Print Loop
    run            Run a JavaScript or TypeScript program
    test           Run tests
    types          Print runtime TypeScript declarations
    upgrade        Upgrade deno executable to given version

    DENO_AUTH_TOKENS     A semi-colon separated list of bearer tokens and
                         hostnames to use when fetching remote modules from
                         private repositories
                         (e.g. ";")
    DENO_CERT            Load certificate authority from PEM encoded file
    DENO_DIR             Set the cache directory
    DENO_INSTALL_ROOT    Set deno installs output directory
                         (defaults to $HOME/.deno/bin)
    DENO_WEBGPU_TRACE    Directory to use for wgpu traces
    HTTP_PROXY           Proxy address for HTTP requests
                         (module downloads, fetch)
    HTTPS_PROXY          Proxy address for HTTPS requests
                         (module downloads, fetch)
    NO_COLOR             Set to disable color
    NO_PROXY             Comma-separated list of hosts which do not use a proxy
                         (module downloads, fetch)

That's all folks - thanks for reading!