DEV Community

Cover image for Deno for JavaScript Beginners
Maximous Black
Maximous Black

Posted on • Updated on • Originally published at

Deno for JavaScript Beginners

So, you're trying to learn JavaScript. You have just gotten a bit fluent with JavaScript in the browser. Then all of a sudden, you come across Deno and the #NodeKiller hype. But you don't know what any of these are. If that's the case, read on!

Before diving in, you need some background information.

What is a JavaScript Engine?

As you may know, JavaScript is an interpreted programming language. It means that source code isn’t compiled into binary code prior to execution.

But how does the computer know what to do with a plain text script?

That’s the job for a JavaScript engine. A JavaScript engine compiles JavaScript code into executable machine code on the fly. This is known a Just In Time (JIT) compilation.

For example, when you run JavaScript on google chrome, your JavaScript engine is V8. If on Mozilla, it is SpiderMonkey.

What is a JavaScript Runtime Environment?

You don’t usually use the JavaScript engine directly. The JavaScript engine works inside an environment, which provides additional features to your JavaScript application that you can use at runtime.

What features?

These can be APIs that allow communicating with the environment outside of the engine.

For example, a web browser like Google Chrome is a desktop JavaScript runtime environment that uses the V8 JavaScript engine and provides DOM API, Fetch API, Storage API, etc.

Similarly, Server-side runtime environments like Node and Deno use the V8 engine and provide File System Access, Network Access, Console, etc.

Why do we need a runtime outside of a browser?

Although the main environment for JavaScript is a web browser, in recent years, JavaScript has taken over the server platforms.

Server-side JavaScript runtime environments give you access to the file system, network, and other things that aren’t allowed in web browsers. You can actually build a whole web application (from the UI to the data layer) with a technology stack based only on JavaScript like MEAN or MERN.

What's wrong with NodeJS?

According to Ryan Dahl (the creator of NodeJS), there were some things NodeJS did wrong. He delivered a presentation about this at JSConf EU 2018.

Not sticking with Promises

NodeJS actually had native promises support but after a few months, it was removed. Due to this NodeJS has to use workarounds for promises implementation.


V8 by itself is a very good security sandbox. NodeJS removes all of those security features and gives the application access to everything.

The Build System

I don't fully understand this one so don't quote me.

Chrome started using GYP for the build system so NodeJS switched too. But later Chrome dropped GYP and adopted GN for their build system as it was faster and simpler. According to Ryan Dahl, the continued usage of GYP is the probably largest failure of NodeJS core.

npm and package.json

All npm packages contain a file, usually in the project root, called package.json - this file holds various metadata relevant to the project.

What's npm

npm or Node Package Manager, as the name suggests, is used to manage dependency packages in your project to make your life easier.

That sounds great! what's the problem with this?

The package.json file has some unnecessary information that is only required by the npm registry. Ryan describes this as "boilerplate noise" as it does not add anything but noise to the project.

npm is centralized and privately controlled. If you have done some projects in the browser, you would know how you link to dependencies. similar to JQuery, Bootstrap, etc. You add any link to the HTML and you can use it directly. In Node, you cannot install dependencies form anywhere but npm.

require("module") without the extension ".js"

This is how you import external libraries, which is not specific enough. For example, if you want to install JQuery in your project, you would first use npm to install it in the project folder using the install command

npm install jquery
Enter fullscreen mode Exit fullscreen mode

Then if you want to use it in a file, you would add a "require()" statement to the file in which you want to use JQuery.


// code that uses JQuery
Enter fullscreen mode Exit fullscreen mode

How is that a problem? It looks neat!

Yeah, but the algorithms, required for this neat syntax to work, are very complex and inefficient. The module loader has to query the file system at multiple locations trying to guess what the user intended.


This is the aftermath of using that neat syntax for importing modules.

When you install dependencies in your project, they get downloaded to the "node_modules" folder.

That makes it neater! I can use them offline! Is that a problem?

The problem is that the dependencies you install, have their own dependencies, and same for them. The dependency tree grows so big, it's hard to manage and store. And you have to do this for every single project, which probably mostly use the same dependencies. There is no way to share dependencies between projects.

Let's say you want to create two different projects but they both use JQuery, you can download "JQuery.js" file and keep it in a shared folder to which you can link from both the projects. And when you are ready to publish the projects, you just change the link to the remote file and publish them. You can even reuse the local file for any future projects. This is not possible in Node.

And if there's a meme about it, then you know it's serious. This is one of the slides from the presentation.



Similar to "index.html", NodeJS would look for an "index.js" file if not specified. This was an unnecessary thing to do. It needlessly complicated the module loading system. It became especially unnecessary after "require()" supported package.json

Why don't they fix these problems?

At this point, all these problems are the core features of NodeJS, and trying to fix them would mean creating a whole new thing. And there is so much code that uses NodeJS that fixing these problems would be the same as a permanent blackout. All old code would become obsolete. Many tech giants use it, many startups use it, many developers use it for personal projects. It's everywhere!

Then why don't they create a whole new thing?

To that, I would like to say:

You don't ask for it until you know you can get it.

NodeJS, when it came out in 2009, was the best thing that could have happened to the web.

And yes, they did create a whole new thing... Deno.

What is Deno?

Deno is a new cross-platform runtime environment, based on Google's V8 engine, just like NodeJS. It's made by the creator of NodeJS, Ryan Dahl. And it is made for the same purpose as NodeJS.

If it's just like NodeJS, what's new in that?

Unlike Node (C++), It's written in Rust, which makes it much faster and safer. It also has many cool new features.

TypeScript support

Deno supports Typescript out of the box. You don't have to set up or configure anything.

What is TypeScript?

TypeScript is a typed superset of JavaScript that transpiles to plain JavaScript. It is developed by Microsoft. Typescript adds many features that make it easier to scale your JavaScript apps and prevent future bugs from the beginning.

You don't need to learn a whole new language for this. Any JavaScript code is a valid typescript code but not the other way around. TypeScript transpiles to clean, simple JavaScript code that runs on any JavaScript engine that supports ECMAScript 3 (or newer).

That's a lot of scripts you're throwing at me. What is ECMAScript?

For now, think of ECMAScript as versions of JavaScript. you can find more information here.

ES modules import syntax

Deno lets you import from the web using ES module syntax, just like you can in the browser.

import { bgBlue, red, bold } from "";
Enter fullscreen mode Exit fullscreen mode

What about the offline usage?

Deno caches the dependencies after it fetches them the first time. So now you don't even have to use a separate local file for development. It all just works. And the cached dependencies can be shared between projects so you use one copy of each dependency for every project you are working on.

This one switch thing solves the whole node_modules problem, makes it faster and helps Deno use the standard JavaScript you use everywhere.

Secure by default

By default, if you run a JavaScript file in Deno, it has no permissions other than read permissions for the project directory. You have to explicitly say yes to all the permissions you want your script to have. It doesn't even have permission to connect to the internet or even your local network. You control what you want your script to do.

That's it? That's all you got?

Most of the changes happened under the hood. The runtime itself got faster, respects browser standard so that it doesn't have to use made-up APIs, got rid of npm, and everything it brought to the table. Stripped all of the unnecessary workarounds and gives you a minimal runtime environment to just get things done.

Node just got destroyed, right?

Wrong! There's one thing, that still keeps Node where it is... age. Over time, Node has gained a lot of users, learning resources, and community support. Deno on the other hand recently hit the version 1.0 milestone. This means it has a very small userbase, not a lot at learning resources, and itself has divided the JavaScript community into two parts.

There is also no standard workflows and development stacks for Deno yet. And it is a long way from tech giants like Google and Microsoft switching to it full time. Which in turn means no jobs related to Deno, because of which, not many people will try to learn it.

So the main thing holding back Deno from being the #NodeKiller is the userbase.

So should I try it out?

Try it out? Yes! Fully commit to it? Not yet!

If you are new to JavaScript, You should definitely learn NodeJS first. In the future, if Deno still proves to be the #NodeKiller, you can switch to Deno easily. All you got to do is ditch the neat import syntax and start feeling responsible for what you make.

Top comments (19)

codemouse92 profile image
Jason C. McDonald • Edited

Thank you for explaining this so well! I have a well-documented hatred of Javascript, and Node beyond that, but you've just made me genuinely interested — and yes, a little excited — in seeing what happens with Deno and the JS landscape now. At last I understand what the hype with Deno is about!

I still won't use any of it. JS gives me hives, though I own that as largely my subjectivity. But now I care about this, and that's a miracle in and of itself, ha ha.

maximousblk profile image
Maximous Black

So happy that you liked it!

warix3 profile image

I haven't tried deno yet but it seems like it doesn't have a single place where all of your dependencies are defined? That used to be package.json but they didn't replace it with anything? It's useful information to see a list of all dependencies of a project instead of having to check through each file to get this information.

maximousblk profile image
Maximous Black • Edited

Yes, Deno does not mandate a single file to list all your dependencies because that would require something like npm to assist that standard. But Deno tries to stay away from the idea of a single entity having control of all of the ecosystem. Deno is a javascript runtime and only a runtime.

For more info, check out this section of deno manual:

It seems unwieldy to import URLs everywhere.

But this creates a problem for package authors who don't have a single place to distribute their packages. Deno authors have a system in place to make up for that, which is just a proxy to GitHub. If you want a more decentralised and immutable (you don't want another left-pad incident, do you?) platform to publish your packages, there is which is a platform independent package registry.

I would highly suggest you try out Deno. It's a step in the right direction. Deno actually prioritises using browser APIs instead of creating custom ones. This unifies the javascript ecosystem to some extent as now it is divided in server-side and client-side javascript, which look and work differently.

mixed_code profile image
Jonathan Atiene

Awesome post I read every line

crash180 profile image
Kevin Eldridge

I did the same. Thank you for taking the time to fix the issues that node and the patches to node to make it work "better" introduced by creating deno

maximousblk profile image
Maximous Black

Thank you so much!

crabmusket profile image
Daniel Buckmaster

Unlike Node (C++), It's written in Rust, which is much faster.

Uh... leaving aside the fact that the actual JS execution is done by V8, which is a) the same as Node and b) written in C++, so really there'll be very little meaningful speed difference - I think it's highly implausible to say Rust is "much faster" than C++, and I say that as a big Rust fan.

maximousblk profile image
Maximous Black • Edited

Agreed and fixed.

From what I have learned so far, Rust is more secure and throws error in compile time unlike C++ which does so in the runtime. This results in developers writing less explicit checks and achieving the same results.

It takes time to perform a check and also increases the binary size when compiled. Rust eliminates such cases while compiling so you don't have to perform any checks at runtime. The speed that comes from reduced runtime checks is what I was talking about, not the raw performance.

Please correct me if this is wrong.

solarliner profile image
🇨🇵️ Nathan Graule • Edited

Rust still performs runtime checking - (vec![0, 1, 2])[3] will throw an error at runtime (even in release mode!), so it doesn't remove all checks. Rust's claim to fame is memory correctness; if the code compiles, the executable is free of memory and concurrency bugs without any garbage collection, however there is still a runtime to Rust (like C and C++).

You don't choose Rust because it's fast. You choose Rust because you want to get as close to the "if it compiles, it works" utopia. Which is paramount for critical software like Deno.

vishnubaliga profile image
Vishnu Baliga

Every piece of line is so informative. Well written!!
I now believe in DENO = Destroy Node :D

yuripredborskiy profile image
Yuri Predborskiy

I still don't get it. You get rid of node modules, and replace it with... Global folder for cached modules? So, basically you just moved node modules folder out of your project folder.

Next, module reusability between projects. Why? Every modern project I've used relies on docker containers or something similar, so there's no reusability, ever. And if you run the app in the cloud, it will, most likely, use a dedicated compute unit for that one app, which just takes this "killer feature" and throws it out the window.

Making deno require access to everything seems cool at first, annoying at second thought. Like, why? Why do you want to limit it to a local folder only? It looks like a sandbox. My little private sandbox... Because js is so unsafe you have to build a bunker to run it?

By the way if it needs permissions to access anything, how many permissions does it need to grab a url with an external module? One, to connect to internet? One, to connect to locally cached file or two, to do both?

To me de-no so far seems not like "destroys node" but more like "node backwards". Hopefully it will grow from this point into something i can pick up and use for a corporate environment because it provides some killer features node simply doesn't have, instead of just trying to be different.

There's one killer feature i see so far - running type script natively. But, at the same time, I don't use TS. Not yet, at least.

I wonder which one happens sooner - deno getting some great use cases or node getting native TS support with debugging out of the box, with no transpiling necessary.

I also wonder if deno can be used as a sandbox for resources that run your js code for testing purposes, like jsfiddle or leetcode. You write your TS code in a web page and it executes elsewhere. Seems interesting to me personally - I won't have to install it locally and will have a chance to run the fiddle without transforming TS to js. Can it be used like that?

maximousblk profile image
Maximous Black

You get rid of node modules, and replace it with... Global folder for cached modules? So, basically you just moved node modules folder out of your project folder...

Exactly. Yes it doesn't help with deployment but it does help while development.

Making deno require access to everything seems cool at first, annoying at second thought. Like, why? Why do you want to limit it to a local folder only? It looks like a sandbox. My little private sandbox... Because js is so unsafe you have to build a bunker to run it?

The fact that Deno allows you to run and install scripts from anywhere on the internet makes it necessary. This probably wasn't the main reason it was made for. Yes it is annoying but you can eliminate that with makefiles or velociraptor (Deno's solution to npm scripts).

One other use case would be if you are working on a project that handles sensitive information, you want to have control over what the project can do. This ensures you don't leak anything during development and you can work with more confidence.

By the way if it needs permissions to access anything, how many permissions does it need to grab a url with an external module? One, to connect to internet? One, to connect to locally cached file or two, to do both?

Deno doesn't need permissions to download and cache modules or to access the project folder. To do anything outside project folder, you need to give explicit permissions.

I also wonder if deno can be used as a sandbox for resources that run your js code for testing purposes, like jsfiddle or leetcode.

There are already online Deno playgrounds popping up. I can't recall at the moment but check out the discord server, they will definitely know many of them.

Thanks for spending time reading my article.

sergix profile image
Peyton McGinnis

abdulghani200 profile image
Abdul Ghani

Indeed informative, thanks for sharing!

maximousblk profile image
Maximous Black • Edited

You're welcome!

miketalbot profile image
Mike Talbot ⭐

I'm hopeful the ecosystem will grow like it must for this to really thrive, still the core reason to use Node. Super exciting, thanks for the full explanation!

sholladay profile image
Info Comment hidden by post author - thread only accessible via permalink
Seth Holladay

If you're looking for a web server framework for Deno that is well tested and documented, try Pogo.

josiasaurel profile image
Josias Aurel

Thanks you for this nice post.

Some comments have been hidden by the post's author - find out more