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MarkBennett / deno-node-compat

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  \/_____/ \/__________/\/_/     \/_/ \/_________/                 \/_/     \/_/ \/_________/     \/_____/ \/__________/

An Gentle Introduction to Using Node Packages in Deno

By @MarkBennett

Comparing Nodejs and Deno

Deno is a new project from Ryan Dhal, the original author of Node.

Node Deno
V8 engine ✅ ✅
ES Modules 🟨 * ✅
Common.js ✅ No
Web APIs 🟨 * ✅
Sandbox / Permissions No ✅
TypeScript No ✅
Linter No ✅
Formatter No ✅
REPL ✅ ✅
npm / node_modules ✅ No
Bundler No ✅
  • Partial support with .mjs files
  • Fetch, Web Crypto, and a growing list of other APIs

Why Care About Deno?

  1. Fast and secure
  2. Betting on Web APIs will pay off
  3. Single executable with TS, linting, formatting, and testing

Learn more at deno.land

Hurdles To Adoption

  1. Most devs know Node
  2. Learning something new is hard
  3. The node/npm ecosystem is much bigger than Deno's

Deno is addressing all of these, and really focused on developer experience.

Hurdles To Adoption

Today going to focus on how Deno is overcoming the third of these, by making Node and npm work seamlessly with Deno.

Running Node code with Deno

Running Node code with Deno

Using packages from npm

Using npm packages is easy!

Just import packages using the npm: url schema and you're good to go!

Never type npm install --save again!

import ?? from "npm:<package-name>[@<version-requirement>]";

Packages are downloaded the first time you import them and cached across the system.

Running Node code with Deno

Using packages from npm

// express-main.ts
import express from "npm:express";

const app = express();

app.get("/", function (_req: Request, res) {
  res.send("Hello World");
});

app.listen(3000);
console.log("listening on http://localhost:3000/");

Running Node code with Deno

Using the Node Standard Library

Node has a large Standard Library which provides access to the file system, network, and more.

Though Deno uses Web APIs, since v1.15 a large portion of the Node Standard Library is available in Deno.

You can access them by importing from the node module in the Deno standard library.

// node-stdlib.ts
import { readFileSync } from "https://deno.land/std@0.158.0/node/fs.ts";
import { stdout } from "https://deno.land/std@0.158.0/node/process.ts";

const data = readFileSync("hello.txt", "utf8");

stdout.write(data);

When you import an npm package, Deno automatically polyfills the Node API for you.

Running Node code with Deno

Running Node binaries

In Deno you run scripts from a url:

deno run main.ts
deno run https://deno.land/std/examples/welcome.ts

Running Node code with Deno

Running Node binaries

Use deno run with an npm:<package-name>[@<version-requirement>][/<binary-name>] url to run a Node package binary.

deno run -A --unstable npm:create-vite-extra
deno run -A --unstable npm:cowsay "Hello!"
deno run -A --unstable npm:cowsay@1.5.0/cowthink "What to eat?"
deno run -A --unstable npm:eslint your_file.js

This is basically the same as using npx in Node since nothing needs to be downloaded or installed first.

  • NOTE: We need to add permissions -A and the --unstable flag to run these scripts.

Running Node code with Deno

Replacing Node scripts

You can also use deno task to run scripts defined in a deno.jsonc file.

// deno.jsonc
{
  "tasks": {
    "fmt": "deno fmt",
    "lint": "deno lint",
    "test": "deno test -A",
    "slides": "slides readme.md"
  }
}

Start the slides with:

deno task slides

This works like the scripts defined in package.json in Node.

Running Node code with Deno

Using Import Maps to port Node source code

When using imports with webpack and node, you can import packages using "bare" specifier (ie "react" or "lodash") and the bundler will resolve the package to the correct file.

// my-node-code.js
import React from "react";
import { map } from "lodash";

Deno doesn't have this feature, but you can use import maps to get the same behavior. They're a standard feature of the browser, which Deno now supports too.

// import-map.json
{
  "imports": {
    "react": "https://cdn.skypack.dev/react",
    "react-dom": "https://cdn.skypack.dev/react-dom"
  }
}

Then just tell Deno about your import map when you run your code:

deno run --import-map ./import_map.json my-node-code.js

Problems You May Run Into

Problems You May Run Into

Missing types

Most packages on npm are missing TypeScript types. This isn't specific to Deno, and you've likely running into it whenever you've used TypeScript with Node.

You can use the @types npm packages to install third-party type definitions.

// express-main.ts
import express from "npm:express";
import type { Request, Response } from "npm:@types/express";

These definitions are not always complete, and you may need to add your own. Pull requests are welcome!

https://github.com/DefinitelyTyped/DefinitelyTyped

Problems You May Run Into

Missing NAPI for loading native modules

Some popular packages like bcrypt and sharp use native Node modules. These let them access C libraries and perform operations that are not possible or optimized in JavaScript.

These aren't currently supported in Deno, but work is underway to add support and the first version was merged into the main branch on Oct 5, 2022.

I'm guessing this will be a headline feature in Deno v1.27.

Problems You May Run Into

Incomplete Node Standard Library polyfills

Though Deno has a large portion of the Node Standard Library available, it's not complete and work is on-going to add more.

You can track progress on GitHub:

And there's a list of missing APIs in the Deno docs:

They're always open to receiving new issues and pull requests!

Problems You May Run Into

Packages expect node_modules

Some packages hard code node_modules into their source (bad!) and won't work without it.

Deno supports this using the --node-modules-dir flag.

// chalk.ts
// this will break without node_modules
import chalk from "npm:chalk@5";

console.log(chalk.green("Hello"));

Can be run with:

deno run --unstable --node-modules-dir chalk.ts

What's Next

Improving Node compatibility

Going forward to the team is already tracking the next Node LTS release. and working to get it's specs passing in Deno.

This is the tracking issue on GitHub:

What's Next

Ultimate goal: Deno as a Node replacement

To get there the Deno team knows they need to have a graceful on-ramp for existing Node developers, and have committed to making it as easy as possible.

Even if Deno doesn't become the next Node, simply pushing Node to better support standards and improve the developer experience is a win for everyone.

What's Next

Getting started

Before you begin, make sure you have Deno installed. You can install it on Mac and Linux with the following command:

curl -fsSL https://deno.land/install.sh | sh

Or with PowerShell on Windows:

irm https://deno.land/install.ps1 | iex

See https://deno.land/#installation for more detials.

What's Next

Getting started

Quickly initialize a new project:

deno init hello-node

This will setup linting, formatting, and testing for your project.

deno run --watch main.ts
deno lint
deno test
deno fmt

What's Next

Getting started

If you're using VS Code, it's also a good idea to install the official Deno extension.

https://marketplace.visualstudio.com/items?itemName=denoland.vscode-deno

See Also

Thank-you

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/ / /____\ \ \/ / /____\/ // / /_______\\ \/___/ /  /_/ /   /\__\/_/___\/ / /____\/ // / /    / / / \ \/___/ /                  /_/\ 
\/________\_\/\/_________/ \/__________/ \_____\/   \_\/    \/_________/\/_________/ \/_/     \/_/   \_____\/                   \_\/

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