Deno Standard Library Essentials

Intermediatev1.0.0

Leverage Deno's standard library for common tasks — file operations, HTTP serving, path manipulation, encoding, and datetime utilities without third-party dependencies.

Content

Overview

Deno's standard library (@std) provides audited, well-tested modules for common programming tasks. Unlike npm packages, these are maintained by the Deno team, follow consistent patterns, and require no dependency management.

Why This Matters

-Audited — reviewed and maintained by the Deno core team
-Consistent — unified API design across all modules
-No dependency hell — standard library has zero external dependencies
-Versioned — stable releases with semver guarantees

Essential Modules

File System Operations

typescript

import { ensureDir, copy, walk } from "@std/fs";
import { join, extname } from "@std/path";

// Create directory tree (like mkdir -p)
await ensureDir("./output/reports");

// Copy files/directories
await copy("./src", "./backup/src", { overwrite: true });

// Walk directory tree
for await (const entry of walk("./src", { exts: [".ts"] })) {
  console.log(entry.path);
}

HTTP Server

typescript

// Modern Deno.serve API (recommended)
Deno.serve({ port: 8000 }, (req) => {
  const url = new URL(req.url);
  if (url.pathname === "/api/health") {
    return Response.json({ status: "ok" });
  }
  return new Response("Not Found", { status: 404 });
});

Encoding & Hashing

typescript

import { encodeBase64, decodeBase64 } from "@std/encoding/base64";
import { crypto } from "@std/crypto";

// Base64 encoding
const encoded = encodeBase64("Hello, World!");
const decoded = new TextDecoder().decode(decodeBase64(encoded));

// Hashing
const data = new TextEncoder().encode("password");
const hash = await crypto.subtle.digest("SHA-256", data);

TOML/YAML/CSV Parsing

typescript

import { parse as parseYaml } from "@std/yaml";
import { parse as parseToml } from "@std/toml";
import { parse as parseCsv } from "@std/csv";

const config = parseYaml(await Deno.readTextFile("config.yaml"));
const settings = parseToml(await Deno.readTextFile("settings.toml"));
const records = parseCsv(await Deno.readTextFile("data.csv"), { skipFirstRow: true });

Assertions (for validation, not just tests)

typescript

import { assertEquals, assertExists } from "@std/assert";

assertExists(Deno.env.get("DATABASE_URL"), "DATABASE_URL is required");

Best Practices

-Prefer @std modules over third-party npm packages when available
-Pin standard library versions in import maps (deno.json)
-Use Deno.serve() for HTTP servers (not std/http/server)
-Use Web Standard APIs (fetch, URL, Response) alongside @std

Common Mistakes

-Using npm packages for tasks the standard library covers
-Not pinning @std versions in deno.json imports
-Using deprecated std modules (check docs for current API)

FAQ

Discussion

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Essential Modules

File System Operations

typescript

import { ensureDir, copy, walk } from "@std/fs";
import { join, extname } from "@std/path";

// Create directory tree (like mkdir -p)
await ensureDir("./output/reports");

// Copy files/directories
await copy("./src", "./backup/src", { overwrite: true });

// Walk directory tree
for await (const entry of walk("./src", { exts: [".ts"] })) {
  console.log(entry.path);
}

HTTP Server

typescript

// Modern Deno.serve API (recommended)
Deno.serve({ port: 8000 }, (req) => {
  const url = new URL(req.url);
  if (url.pathname === "/api/health") {
    return Response.json({ status: "ok" });
  }
  return new Response("Not Found", { status: 404 });
});

Encoding & Hashing

typescript

import { encodeBase64, decodeBase64 } from "@std/encoding/base64";
import { crypto } from "@std/crypto";

// Base64 encoding
const encoded = encodeBase64("Hello, World!");
const decoded = new TextDecoder().decode(decodeBase64(encoded));

// Hashing
const data = new TextEncoder().encode("password");
const hash = await crypto.subtle.digest("SHA-256", data);

TOML/YAML/CSV Parsing

typescript

import { parse as parseYaml } from "@std/yaml";
import { parse as parseToml } from "@std/toml";
import { parse as parseCsv } from "@std/csv";

const config = parseYaml(await Deno.readTextFile("config.yaml"));
const settings = parseToml(await Deno.readTextFile("settings.toml"));
const records = parseCsv(await Deno.readTextFile("data.csv"), { skipFirstRow: true });

Assertions (for validation, not just tests)

typescript

import { assertEquals, assertExists } from "@std/assert";

assertExists(Deno.env.get("DATABASE_URL"), "DATABASE_URL is required");