Syntax Highlighting Showcase

JavaScript

javascript

async function fetchUserData(userId) {
  const response = await fetch(`/api/users/${userId}`);
  if (!response.ok) {
    throw new Error(`HTTP error! status: ${response.status}`);
  }
  const data = await response.json();
  return { ...data, fetchedAt: Date.now() };
}

// Destructuring, template literals, arrow functions
const formatUser = ({ name, email, roles = [] }) =>
  `${name} <${email}> [${roles.join(', ')}]`;

class EventEmitter {
  #listeners = new Map();

  on(event, callback) {
    if (!this.#listeners.has(event)) {
      this.#listeners.set(event, []);
    }
    this.#listeners.get(event).push(callback);
    return this;
  }

  emit(event, ...args) {
    for (const cb of this.#listeners.get(event) ?? []) {
      cb(...args);
    }
  }
}

TypeScript

typescript

interface Repository<T extends { id: string }> {
  findById(id: string): Promise<T | null>;
  findAll(filter?: Partial<T>): Promise<T[]>;
  create(data: Omit<T, 'id'>): Promise<T>;
  update(id: string, data: Partial<T>): Promise<T>;
  delete(id: string): Promise<void>;
}

type Result<T, E = Error> =
  | { ok: true; value: T }
  | { ok: false; error: E };

async function tryCatch<T>(fn: () => Promise<T>): Promise<Result<T>> {
  try {
    return { ok: true, value: await fn() };
  } catch (error) {
    return { ok: false, error: error as Error };
  }
}

// Mapped type with conditional
type ReadonlyDeep<T> = {
  readonly [K in keyof T]: T[K] extends object ? ReadonlyDeep<T[K]> : T[K];
};

Python

python

from dataclasses import dataclass, field
from typing import Generator
import asyncio

@dataclass
class TreeNode:
    value: int
    left: "TreeNode | None" = None
    right: "TreeNode | None" = None

    def inorder(self) -> Generator[int, None, None]:
        if self.left:
            yield from self.left.inorder()
        yield self.value
        if self.right:
            yield from self.right.inorder()

async def fetch_all(urls: list[str]) -> list[dict]:
    async with aiohttp.ClientSession() as session:
        tasks = [session.get(url) for url in urls]
        responses = await asyncio.gather(*tasks)
        return [await r.json() for r in responses]

# List comprehension with walrus operator
results = [
    cleaned
    for raw in data
    if (cleaned := raw.strip().lower()) and len(cleaned) > 3
]

Rust

rust

use std::collections::HashMap;

#[derive(Debug, Clone)]
struct LRUCache<K: Eq + std::hash::Hash + Clone, V: Clone> {
    capacity: usize,
    map: HashMap<K, (V, usize)>,
    counter: usize,
}

impl<K: Eq + std::hash::Hash + Clone, V: Clone> LRUCache<K, V> {
    fn new(capacity: usize) -> Self {
        Self {
            capacity,
            map: HashMap::with_capacity(capacity),
            counter: 0,
        }
    }

    fn get(&mut self, key: &K) -> Option<&V> {
        self.counter += 1;
        if let Some(entry) = self.map.get_mut(key) {
            entry.1 = self.counter;
            Some(&entry.0)
        } else {
            None
        }
    }

    fn put(&mut self, key: K, value: V) {
        if self.map.len() >= self.capacity && !self.map.contains_key(&key) {
            let oldest = self.map.iter()
                .min_by_key(|(_, (_, ts))| ts)
                .map(|(k, _)| k.clone());
            if let Some(k) = oldest {
                self.map.remove(&k);
            }
        }
        self.counter += 1;
        self.map.insert(key, (value, self.counter));
    }
}

Go

package main

import (
	"context"
	"fmt"
	"sync"
	"time"
)

type WorkerPool struct {
	workers int
	jobs    chan func() error
	wg      sync.WaitGroup
}

func NewWorkerPool(workers int) *WorkerPool {
	return &WorkerPool{
		workers: workers,
		jobs:    make(chan func() error, workers*2),
	}
}

func (p *WorkerPool) Start(ctx context.Context) <-chan error {
	errs := make(chan error, p.workers)

	for i := 0; i < p.workers; i++ {
		p.wg.Add(1)
		go func(id int) {
			defer p.wg.Done()
			for {
				select {
				case <-ctx.Done():
					return
				case job, ok := <-p.jobs:
					if !ok {
						return
					}
					if err := job(); err != nil {
						errs <- fmt.Errorf("worker %d: %w", id, err)
					}
				}
			}
		}(i)
	}

	go func() {
		p.wg.Wait()
		close(errs)
	}()

	return errs
}

Java

java

import java.util.concurrent.ConcurrentHashMap;
import java.util.function.Function;

public sealed interface Either<L, R> permits Either.Left, Either.Right {

    record Left<L, R>(L value) implements Either<L, R> {}
    record Right<L, R>(R value) implements Either<L, R> {}

    static <L, R> Either<L, R> left(L value) {
        return new Left<>(value);
    }

    static <L, R> Either<L, R> right(R value) {
        return new Right<>(value);
    }

    default <T> T fold(Function<L, T> onLeft, Function<R, T> onRight) {
        return switch (this) {
            case Left<L, R> l -> onLeft.apply(l.value());
            case Right<L, R> r -> onRight.apply(r.value());
        };
    }

    default <T> Either<L, T> map(Function<R, T> f) {
        return switch (this) {
            case Left<L, R> l -> Either.left(l.value());
            case Right<L, R> r -> Either.right(f.apply(r.value()));
        };
    }
}

C / C++

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct Node {
    void *data;
    struct Node *next;
} Node;

typedef struct {
    Node *head;
    size_t size;
    size_t elem_size;
} LinkedList;

LinkedList *list_create(size_t elem_size) {
    LinkedList *list = malloc(sizeof(LinkedList));
    list->head = NULL;
    list->size = 0;
    list->elem_size = elem_size;
    return list;
}

void list_push(LinkedList *list, const void *data) {
    Node *node = malloc(sizeof(Node));
    node->data = malloc(list->elem_size);
    memcpy(node->data, data, list->elem_size);
    node->next = list->head;
    list->head = node;
    list->size++;
}

Ruby

ruby

module Enumerable
  def lazy_map(&block)
    Enumerator::Lazy.new(self) do |yielder, value|
      yielder << block.call(value)
    end
  end
end

class Router
  attr_reader :routes

  def initialize(&block)
    @routes = []
    instance_eval(&block) if block_given?
  end

  %i[get post put patch delete].each do |method|
    define_method(method) do |path, **opts, &handler|
      @routes << {
        method: method.upcase,
        pattern: compile_pattern(path),
        handler: handler,
        **opts
      }
    end
  end

  private

  def compile_pattern(path)
    regex = path.gsub(/:(\w+)/) { "(?<#{$1}>[^/]+)" }
    Regexp.new("\\A#{regex}\\z")
  end
end

SQL

sql

WITH monthly_revenue AS (
    SELECT
        date_trunc('month', o.created_at) AS month,
        p.category,
        SUM(oi.quantity * oi.unit_price) AS revenue,
        COUNT(DISTINCT o.customer_id) AS unique_customers
    FROM orders o
    JOIN order_items oi ON o.id = oi.order_id
    JOIN products p ON oi.product_id = p.id
    WHERE o.status = 'completed'
        AND o.created_at >= NOW() - INTERVAL '12 months'
    GROUP BY 1, 2
),
ranked AS (
    SELECT *,
        ROW_NUMBER() OVER (
            PARTITION BY month ORDER BY revenue DESC
        ) AS rank,
        LAG(revenue) OVER (
            PARTITION BY category ORDER BY month
        ) AS prev_month_revenue
    FROM monthly_revenue
)
SELECT
    month,
    category,
    revenue,
    unique_customers,
    ROUND(
        (revenue - prev_month_revenue) / NULLIF(prev_month_revenue, 0) * 100,
        2
    ) AS growth_pct
FROM ranked
WHERE rank <= 5
ORDER BY month DESC, revenue DESC;

Shell / Bash

bash

#!/usr/bin/env bash
set -euo pipefail

readonly LOG_FILE="/var/log/deploy.log"
readonly LOCK_FILE="/tmp/deploy.lock"

log() {
  local level="$1"; shift
  printf "[%s] [%s] %s\n" "$(date -u +%Y-%m-%dT%H:%M:%SZ)" "$level" "$*" \
    | tee -a "$LOG_FILE"
}

cleanup() {
  rm -f "$LOCK_FILE"
  log INFO "Lock released"
}
trap cleanup EXIT

deploy() {
  local env="${1:?Environment required}"
  local version="${2:-latest}"

  if [[ -f "$LOCK_FILE" ]]; then
    log ERROR "Deployment already in progress"
    return 1
  fi
  echo $$ > "$LOCK_FILE"

  log INFO "Deploying version=$version to env=$env"

  docker pull "app:${version}" \
    && docker compose -f "docker-compose.${env}.yml" up -d \
    && log INFO "Deployment successful" \
    || { log ERROR "Deployment failed"; return 1; }
}

deploy "$@"

HTML / CSS

html

<dialog id="modal" class="backdrop:bg-black/50">
  <form method="dialog">
    <header>
      <h2>Confirm Action</h2>
      <button type="submit" value="cancel" aria-label="Close">
        &times;
      </button>
    </header>
    <p>Are you sure you want to proceed?</p>
    <footer>
      <button type="submit" value="cancel">Cancel</button>
      <button type="submit" value="confirm" autofocus>Confirm</button>
    </footer>
  </form>
</dialog>

css

@layer components {
  .card {
    --card-padding: clamp(1rem, 3vw, 2rem);

    display: grid;
    grid-template-rows: auto 1fr auto;
    padding: var(--card-padding);
    border-radius: 0.75rem;
    background: light-dark(white, oklch(0.25 0.01 260));
    box-shadow: 0 1px 3px oklch(0 0 0 / 0.12);
    transition: box-shadow 0.2s ease;

    &:hover {
      box-shadow: 0 8px 24px oklch(0 0 0 / 0.15);
    }

    & > img {
      aspect-ratio: 16 / 9;
      object-fit: cover;
      border-radius: 0.5rem;
    }
  }
}

JSON / YAML

json

{
  "compilerOptions": {
    "target": "ES2022",
    "module": "NodeNext",
    "strict": true,
    "paths": {
      "@/*": ["./src/*"],
      "@components/*": ["./src/components/*"]
    },
    "plugins": [{ "name": "next" }]
  },
  "include": ["src/**/*.ts", "src/**/*.tsx"],
  "exclude": ["node_modules"]
}

yaml

services:
  app:
    build:
      context: .
      dockerfile: Dockerfile
      args:
        NODE_ENV: production
    ports:
      - "3000:3000"
    environment:
      DATABASE_URL: postgres://user:pass@db:5432/app
    depends_on:
      db:
        condition: service_healthy
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost:3000/health"]
      interval: 30s
      retries: 3

  db:
    image: postgres:16-alpine
    volumes:
      - pgdata:/var/lib/postgresql/data
    environment:
      POSTGRES_DB: app
      POSTGRES_USER: user
      POSTGRES_PASSWORD: pass

volumes:
  pgdata:

Diff

diff

--- a/src/config.ts
+++ b/src/config.ts
@@ -12,8 +12,10 @@ export const config = {
   pagination: {
     posts: 10,
-    series: 5,
+    series: 12,
   },
+  features: {
+    darkMode: true,
+    search: true,
+  },
 };

Inline Code

Inline code also renders with highlighting: const x: number = 42, a CSS property like background-color: oklch(0.5 0.2 240), or a shell command git rebase -i HEAD~3.