Deno - The easiest, most secure JavaScript runtime
Introduction
In 2020 I wrote an initial article covering some topics about Deno, its advantages and disadvantages. Since then the tool has evolved quite a bit, and with that I will bring some content covering development with Deno. In this article I will present some basic examples that demonstrate Deno's capabilities.
Installation
Deno provides several installation options:
Mac & Linux
curl -fsSL https://deno.land/x/install/install.sh | sh
Windows
choco install deno
First Steps
Deno is a JavaScript/TypeScript runtime that tries to be compatible with modern browsers, so a console.log can be run in Deno and in a browser.
function capitalize(word) {
return word.charAt(0).toUpperCase() + word.slice(1);
}
function hello(name) {
return "Hello " + capitalize(name);
}
console.log(hello("john"));
console.log(hello("Sarah"));
console.log(hello("kai"));
hello-world.js
To run the file above type: deno run hello-world.js
The output will be:
Hello John
Hello Sarah
Hello Kai
The same file can be rewritten in TS, since Deno ships it natively, without the need for installation/configuration.
Dependencies
Deno uses URLs for dependency management.
A convention is that all dependency URLs are in the same place called deps.ts. Dependencies are exported to be used in other locations.
And dev dependencies go in dev_deps.ts.
It is important to note that this is just a convention, but it can be done in whatever way is best for the project/development team.
Example to create a file to calculate the total cost of an operation
First I will create the deps.ts file, exporting some functionality from the ramda lib, as below:
export {
add,
multiply,
} from "https://x.nest.land/ramda@0.27.0/source/index.js"
Then I created the arithmetic.ts file importing add and multiply from the deps.ts file.
import { add, multiply } from "./deps.ts"
function totalCost(outbound: number, inbound: number, tax: number): number {
return multiply(add(outbound, inbound), tax);
}
console.log(totalCost(19, 31, 1.2));
console.log(totalCost(45, 27, 1.15));
The example above is quite simple: I pass 3 arguments — outbound, inbound, and tax — to calculate the total cost of an operation. Result:
/**
* Output
*
* 60
* 82.8
*/
Fetch Data
Just like in browsers, Deno implements web standards, so it is possible to perform a fetch data using the fetch API.
/**
* Output: JSON Data
*/
const jsonResponse = await fetch("https://api.github.com/users/denoland");
const jsonData = await jsonResponse.json();
console.log(jsonData);
/**
* Output: HTML Data
*/
const textResponse = await fetch("https://deno.land/");
const textData = await textResponse.text();
console.log(textData);
/**
* Output: Error Message
*/
try {
await fetch("https://does.not.exist/");
} catch (error) {
console.log(error);
}
fetch.ts
Deno by default has a security layer for IO (input/output) control, making it inaccessible. Therefore, it is necessary to explicitly grant this access permission to the script. In this way, to run the script above it is necessary to grant a network permission --allow-net, so I can make the HTTP requests.
To learn more about Deno's permissions, visit Permissions
Conclusion
As you can see, the learning curve for Deno is very low for those who already know JavaScript/TypeScript. Those who work with/know Node will notice countless similarities, but the big differences are mainly the security layer and the way packages are imported (without installation, without creating a node_modules).
Deno is very simple and easy to learn; this is just an initial article with some features and a first look at the tool. Of course, using it in production everything I listed here expands quite a bit and it is necessary to go deep into many other points that I haven't even mentioned here.
But for this initial article I just wanted to bring some examples and show how the tool works.
All the examples described here were taken from Deno's own documentation.