Lesson 15-Deno Commonly Used Basic Modules and Standard Library

Deno’s standard library (std/) provides a rich set of out-of-the-box modules, adhering to modern JavaScript/TypeScript best practices. Below is a categorized overview of core modules and their functionalities:

Core Foundation Modules

File System Operations (std/fs)

Features:

• All operations require explicit --allow-read/--allow-write permissions.
• Supports Promise-based asynchronous APIs.
• Provides atomic operations (e.g., copy with overwrite option).

Network Requests (std/http)

Typical Usage:

// Create a basic HTTP server
import { serve } from "std/http/server.ts";
const server = serve({ port: 8000 });
for await (const req of server) {
  req.respond({ body: "Hello Deno!" });
}

// Create a basic HTTP server
import { serve } from "std/http/server.ts";
const server = serve({ port: 8000 });
for await (const req of server) {
  req.respond({ body: "Hello Deno!" });
}

Path Handling (std/path)

Key Functions:

• join(...paths): Smart path concatenation.
• basename(path): Extract filename.
• extname(path): Extract file extension.

Advanced Functionality Modules

Data Parsing (std/encoding)

Notes:

• JSON operations use the global JSON object (consistent with browsers).
• Base64 supports URL-safe mode.

Date and Time (std/datetime)

Unique Features:

• Supports multiple date parsing formats.
• Time zone conversion utilities.

Logging System (std/log)

Log Levels:

• DEBUG | INFO | WARNING | ERROR | CRITICAL

Utility Modules

Testing Framework (std/testing)

Assertion Methods:

• assertEquals(actual, expected)
• assertThrows(fn, ErrorClass?)

Random Number Generation (std/random)

Security Note:

• randomBytes uses OS-level cryptographically secure APIs.
• Suitable for generating keys, tokens, and other sensitive data.

Signal Handling (std/signal)

Supported Signals:

• SIGINT (Ctrl+C)
• SIGTERM (Graceful termination)

Web Development Related

Web Utilities (std/web)

Use Cases:

• Frontend compatibility in Deno Deploy environments.
• Server-side simulation of browser APIs.

Best Practices for Module Usage

Centralized Dependency Management (deps.ts)

// deps.ts
export { serve } from "https://deno.land/std@0.140.0/http/server.ts"
export { assertEquals } from "https://deno.land/std@0.140.0/testing/asserts.ts"

// main.ts
import { serve, assertEquals } from "./deps.ts"

// deps.ts
export { serve } from "https://deno.land/std@0.140.0/http/server.ts"
export { assertEquals } from "https://deno.land/std@0.140.0/testing/asserts.ts"

// main.ts
import { serve, assertEquals } from "./deps.ts"

Advantages:

• Unified version control.
• Simplified import paths.

Principle of Least Privilege

# Grant only necessary permissions
deno run --allow-net=api.example.com --allow-read=./data main.ts

# Grant only necessary permissions
deno run --allow-net=api.example.com --allow-read=./data main.ts

Security Recommendations:

• Avoid using --allow-all.
• Fine-tune permission scopes (e.g., specify allowed domains).

Leveraging the Caching Mechanism

# Manually pre-cache dependencies
deno cache --import-map=import_map.json main.ts

# View cache location
deno info

# Manually pre-cache dependencies
deno cache --import-map=import_map.json main.ts

# View cache location
deno info

Cache Directory:

• Defaults to ~/.deno/dir (customizable via DENO_DIR environment variable).

Standard Library Updates and Version Control

Version Specification:

// Use specific version
import { serve } from "https://deno.land/std@0.140.0/http/server.ts"

// Or manage uniformly via import map
{
  "imports": {
    "std/": "https://deno.land/std@0.140.0/"
  }
}

// Use specific version
import { serve } from "https://deno.land/std@0.140.0/http/server.ts"

// Or manage uniformly via import map
{
  "imports": {
    "std/": "https://deno.land/std@0.140.0/"
  }
}

Upgrade Strategy:

• Regularly check official release notes.
• Use deno upgrade to update the runtime.

By effectively combining these standard library modules, developers can rapidly build high-performance, secure Deno applications while maintaining code simplicity and maintainability.