Deno: The TypeScript Runtime That Makes Python Developers Jealous

2025-05-05

Scripting languages solve everyday problems for developers, but they come with tradeoffs. Python, despite its popularity, struggles with packaging, performance, and bolted-on type systems. Deno solves these problems with first-class TypeScript support, V8 performance, and a security-first approach – all while enabling standalone executable compilation that eliminates dependency nightmares.

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Why Consider Deno in 2025?

Deno represents the natural evolution of JavaScript runtimes, addressing many of Node.js's shortcomings while leveraging modern development practices. Created by Ryan Dahl (the original creator of Node.js), Deno brings a "batteries included" approach to runtime development with built-in TypeScript support, security controls, and modern tooling.

A Fresh Alternative to Python's Challenges

Python has dominated the scripting world for years, but increasingly shows its age:

Package management remains fragmented despite improvements with tools like UV
The Global Interpreter Lock (GIL) limits true parallelism
Type annotations feel bolted-on rather than integrated
Asynchronous programming is awkward compared to JavaScript's native approach

Deno offers a compelling alternative that feels familiar to JavaScript developers while addressing these pain points.

Practical Deno: Building CLI Tools

Let's examine a simple yet practical example: a "Marco Polo" CLI application built with Deno. This demonstrates Deno's straightforward approach to building command-line tools.

/**
 * Marco Polo CLI
 * Responds with "Polo" when given "Marco" as the name argument
 */

/**
 * Parses command line arguments for the name flag
 * @returns The value of the --name argument or undefined if not provided
 */
function parseArgs(): string | undefined {
  const args = Deno.args;
  const nameIndex = args.findIndex(arg => arg === "--name");
  
  if (nameIndex !== -1 && nameIndex + 1 < args.length) {
    return args[nameIndex + 1];
  }
  
  return undefined;
}

/**
 * Handles the Marco Polo game logic
 * @param name The name input to check
 * @returns Response message based on the name
 */
export function handleMarcoPolo(name: string): string {
  if (!name) {
    return "Please provide a name using --name";
  }
  
  if (name.toLowerCase() === "marco") {
    return "Polo!";
  }
  
  return `Hello, ${name}! Say "Marco" to play the game.`;
}

/**
 * Main function that runs the CLI
 */
function main(): void {
  const name = parseArgs();
  const response = handleMarcoPolo(name || "");
  console.log(response);
}

// Run the main function if this is the main module
if (import.meta.main) {
  main();
}

This simple program demonstrates several Deno features:

Native TypeScript support with no configuration
Access to command-line arguments through Deno.args
Clean module system with import.meta.main to determine if a file is the entry point
Clear type annotations that improve code quality

Testing in Deno

Deno includes a built-in testing framework that makes writing tests straightforward:

import { assertEquals } from "https://deno.land/std/assert/mod.ts";
import { handleMarcoPolo } from "./marco-polo.ts";

Deno.test("marco-polo responds with 'Polo!' for 'Marco'", () => {
  assertEquals(handleMarcoPolo("Marco"), "Polo!");
});

Deno.test("marco-polo responds with 'Polo!' for 'marco' (case insensitive)", () => {
  assertEquals(handleMarcoPolo("marco"), "Polo!");
});

Deno.test("marco-polo provides help message for empty name", () => {
  assertEquals(handleMarcoPolo(""), "Please provide a name using --name");
});

Deno.test("marco-polo provides friendly message for other names", () => {
  const name = "Alice";
  assertEquals(handleMarcoPolo(name), `Hello, ${name}! Say "Marco" to play the game.`);
});

Notice how:

Tests are defined using the built-in Deno.test function
Standard library imports use URLs directly (no package.json or npm install)
Assertions are clear and TypeScript-aware
Running tests is as simple as deno test

Streamlined Build Process

With Deno, you can easily create a build process using familiar tools like Make:

.PHONY: all lint format test build clean

# Default target
all: lint format test build

# Source files
SRC_DIR := .
SRC_FILES := $(shell find $(SRC_DIR) -name "*.ts" -not -path "*/\.*")
HELLO_ENTRY := hello-world.ts
MARCO_ENTRY := marco-polo.ts
HELLO_OUTPUT := dist/hello-world
MARCO_OUTPUT := dist/marco-polo

# Lint TypeScript files
lint:
	deno lint $(SRC_DIR)

# Format TypeScript files
format:
	deno fmt $(SRC_DIR)

# Run tests
test:
	deno test

# Check types
check:
	deno check $(SRC_FILES)

# Build standalone JavaScript
build: build-hello build-marco

build-hello:
	mkdir -p dist
	deno compile --output $(HELLO_OUTPUT) $(HELLO_ENTRY)

build-marco:
	mkdir -p dist
	deno compile --output $(MARCO_OUTPUT) $(MARCO_ENTRY)

# Run the programs (for development)
run-hello:
	deno run --allow-net $(HELLO_ENTRY)

run-marco:
	deno run $(MARCO_ENTRY) --name "Marco"

# Clean built files
clean:
	rm -rf dist

This Makefile demonstrates:

Built-in formatting with deno fmt
Built-in linting with deno lint
Type checking with deno check
Compiling to standalone executables with deno compile
Running programs with explicit permissions using deno run

Key Benefits Over Python

Built-in TypeScript Support: While Python added type hints as an afterthought, TypeScript was designed with types from the beginning. Deno embraces this with first-class TypeScript support:
- No transpilation step or additional tooling needed
- Types help catch errors before runtime
- Better IDE support with autocompletion and error detection
- Type definitions included for the standard library
Superior Performance: Deno leverages the V8 JavaScript engine for significant performance benefits:
- JIT compilation optimizations provide faster execution than CPython
- No Global Interpreter Lock limiting parallelism
- Asynchronous operations are first-class citizens
- Better memory management with V8's garbage collector
- Higher throughput for I/O-bound operations
Zero Dependencies Philosophy: Deno rethinks package management:
- No package.json or external package manager required
- URLs serve as imports, simplifying dependency management
- Built-in standard library for common operations
- Versioned dependencies in code, not separate files
- No equivalent to the notorious node_modules folder
Modern Security Model: Security is built into Deno from the ground up:
- Explicit permissions for file, network, and environment access
- Granular permission control compared to Python's all-or-nothing approach
- Secure by default—scripts cannot access system resources without permission
- Sandboxed execution environment
- Permission prompts during execution
Simplified Bundling and Distribution: Perhaps Deno's most compelling feature:
- Compile to standalone executables with deno compile
- Consistent execution across platforms
- No need for virtual environments
- No interpreter required on target systems
- Simplified deployment to production
Developer Experience: Deno includes tools that developers need:
- Built-in testing framework
- Code formatting with deno fmt
- Documentation generation
- Dependency inspection
- LSP (Language Server Protocol) support
- Comprehensive debugging tools

Real-World Usage Scenarios

DevOps Tooling

Replace Python scripts with more performant, type-safe alternatives:

// deployment-status.ts
// Run with: deno run --allow-net --allow-env deployment-status.ts

import { parseArgs } from "https://deno.land/std/flags/mod.ts";

const { service = "all", environment = "production" } = parseArgs(Deno.args);

async function checkServiceStatus(service: string, env: string): Promise<string> {
  // In a real implementation, this would make API calls to your infrastructure
  console.log(`Checking status of ${service} in ${env} environment...`);
  return "Healthy";
}

async function main() {
  const status = await checkServiceStatus(service, environment);
  console.log(`Status: ${status}`);
}

if (import.meta.main) {
  main().catch(console.error);
}

Data Processing

Leverage V8's performance for data transformation with strong typing:

// process-logs.ts
// Run with: deno run --allow-read=./logs --allow-write=./output process-logs.ts

interface LogEntry {
  timestamp: string;
  level: "INFO" | "WARN" | "ERROR";
  message: string;
}

async function processLogs(inputDir: string, outputFile: string) {
  const decoder = new TextDecoder("utf-8");
  const entries: LogEntry[] = [];
  
  for await (const dirEntry of Deno.readDir(inputDir)) {
    if (dirEntry.isFile && dirEntry.name.endsWith('.log')) {
      const content = decoder.decode(await Deno.readFile(`${inputDir}/${dirEntry.name}`));
      const lines = content.split('\n').filter(line => line.trim());
      
      for (const line of lines) {
        // Parse log line (simplified example)
        const [timestamp, level, message] = line.split('|');
        if (timestamp && level && message) {
          entries.push({
            timestamp,
            level: level as "INFO" | "WARN" | "ERROR",
            message: message.trim()
          });
        }
      }
    }
  }
  
  // Process entries (e.g., filter, transform)
  const errorEntries = entries.filter(entry => entry.level === "ERROR");
  
  // Write output
  await Deno.writeTextFile(
    outputFile,
    JSON.stringify(errorEntries, null, 2)
  );
  
  console.log(`Processed ${entries.length} log entries, found ${errorEntries.length} errors`);
}

if (import.meta.main) {
  processLogs("./logs", "./output/errors.json").catch(console.error);
}

Microservices

Build lightweight API services with excellent performance characteristics:

// simple-api.ts
// Run with: deno run --allow-net simple-api.ts

import { serve } from "https://deno.land/std/http/server.ts";

type User = {
  id: number;
  name: string;
  email: string;
};

// In-memory database for demo
const users: User[] = [
  { id: 1, name: "Alice", email: "alice@example.com" },
  { id: 2, name: "Bob", email: "bob@example.com" },
];

async function handler(req: Request): Promise<Response> {
  const url = new URL(req.url);
  
  // GET /users
  if (req.method === "GET" && url.pathname === "/users") {
    return new Response(JSON.stringify(users), {
      headers: { "Content-Type": "application/json" }
    });
  }
  
  // GET /users/:id
  if (req.method === "GET" && url.pathname.match(/^\/users\/\d+$/)) {
    const id = parseInt(url.pathname.split("/")[2]);
    const user = users.find(u => u.id === id);
    
    if (user) {
      return new Response(JSON.stringify(user), {
        headers: { "Content-Type": "application/json" }
      });
    }
    
    return new Response(JSON.stringify({ error: "User not found" }), {
      status: 404,
      headers: { "Content-Type": "application/json" }
    });
  }
  
  return new Response(JSON.stringify({ error: "Not found" }), {
    status: 404,
    headers: { "Content-Type": "application/json" }
  });
}

console.log("Server running at http://localhost:8000");
await serve(handler, { port: 8000 });

Deno and Rust: Perfect Companions

Deno itself is built with Rust, showcasing how these technologies complement each other:

Shared Philosophy: Both focus on safety, performance, and developer experience.
Development Velocity: Use TypeScript/Deno for rapid prototyping and high-level application logic, while reserving Rust for performance-critical sections.
Interoperability: Deno can call compiled Rust functions via WebAssembly, and Rust can be used to build custom Deno modules.
Progressive Optimization Path: Start with Deno for an MVP, then selectively optimize critical paths with Rust as needed.

Getting Started with Deno

Installation:

# On macOS/Linux using Shell:
curl -fsSL https://deno.land/x/install/install.sh | sh

# On Windows using PowerShell:
iwr https://deno.land/x/install/install.ps1 -useb | iex

Create a simple script:

// hello.ts
console.log("Hello from Deno!");

Run it:
```
deno run hello.ts
```
Compile to a standalone executable:
```
deno compile hello.ts
```

Conclusion

In 2025, Deno represents a compelling alternative to Python for scripting tasks, CLI tools, and web services. Its combination of TypeScript's type safety, V8's performance, and modern security features addresses many long-standing pain points in the scripting ecosystem.

By adopting the "batteries included" philosophy while maintaining a security-first approach, Deno delivers a developer experience that feels both familiar and refreshingly modern. The ability to compile scripts to standalone executables eliminates the deployment headaches that have plagued Python for years.

Whether you're building DevOps tooling, microservices, or data processing pipelines, Deno deserves a place in your technology toolkit – especially if you're already comfortable with JavaScript/TypeScript or looking for a more modern alternative to Python.