Deno TypeScript Development with Claude Code

Streamlining Deno Development With Claude Code

Deno is a security-first modern runtime. It supports TypeScript natively and provides a safe execution environment through its permission model. Combined with Claude Code, you can quickly take advantage of Deno’s unique features.

Initial Project Setup

> Create a web app with Deno.
> Use the Fresh framework and configure deno.json.

// deno.json
{
  "lock": false,
  "tasks": {
    "dev": "deno run -A --watch=static/,routes/ dev.ts",
    "build": "deno run -A dev.ts build",
    "start": "deno run -A main.ts",
    "test": "deno test -A --coverage=coverage",
    "lint": "deno lint",
    "fmt": "deno fmt"
  },
  "imports": {
    "$fresh/": "https://deno.land/x/[email protected]/",
    "$std/": "https://deno.land/[email protected]/",
    "preact": "https://esm.sh/[email protected]",
    "preact/": "https://esm.sh/[email protected]/"
  },
  "compilerOptions": {
    "jsx": "react-jsx",
    "jsxImportSource": "preact"
  }
}

Using the Permission Model

By default, Deno denies all access.

> Create an API server that only allows file reads and network access.
> Use the principle of least privilege.

// server.ts
// Run with: deno run --allow-net=:8000 --allow-read=./data server.ts

import { serve } from "$std/http/server.ts";

const handler = async (req: Request): Promise<Response> => {
  const url = new URL(req.url);

  if (url.pathname === "/api/config") {
    const data = await Deno.readTextFile("./data/config.json");
    return new Response(data, {
      headers: { "content-type": "application/json" },
    });
  }

  if (url.pathname === "/api/items") {
    const dir = Deno.readDir("./data/items");
    const items = [];
    for await (const entry of dir) {
      if (entry.isFile && entry.name.endsWith(".json")) {
        const content = await Deno.readTextFile(
          `./data/items/${entry.name}`
        );
        items.push(JSON.parse(content));
      }
    }
    return Response.json(items);
  }

  return new Response("Not Found", { status: 404 });
};

serve(handler, { port: 8000 });

Island Architecture With Fresh

> Create a counter using Fresh's island components.
> Be deliberate about the server/client split.

// routes/index.tsx
import Counter from "../islands/Counter.tsx";

export default function Home() {
  return (
    <div class="max-w-screen-md mx-auto p-4">
      <h1 class="text-4xl font-bold">Deno Fresh App</h1>
      <Counter start={0} />
    </div>
  );
}

// islands/Counter.tsx
import { useSignal } from "@preact/signals";

interface CounterProps {
  start: number;
}

export default function Counter({ start }: CounterProps) {
  const count = useSignal(start);
  return (
    <div class="flex gap-4 items-center">
      <button onClick={() => count.value--}>-</button>
      <span class="text-2xl">{count}</span>
      <button onClick={() => count.value++}>+</button>
    </div>
  );
}

Tests and Coverage

// server_test.ts
import { assertEquals } from "$std/assert/assert_equals.ts";

Deno.test("API health check", async () => {
  const res = await fetch("http://localhost:8000/api/config");
  assertEquals(res.status, 200);
  const data = await res.json();
  assertEquals(typeof data, "object");
});

Deno.test("file operations with permissions", async () => {
  const content = await Deno.readTextFile("./data/config.json");
  const config = JSON.parse(content);
  assertEquals(config.version !== undefined, true);
});

Deploying to Deno Deploy

# Deno Deploy CLI
deno install -A jsr:@deno/deployctl

# Deploy
deployctl deploy --project=my-app --entrypoint=main.ts

Summary

Deno’s security model and native TypeScript support deliver a safe and pleasant developer experience. With Claude Code, you can efficiently get comfortable with permission configuration and Fresh’s patterns. Also see TypeScript tips and the security audit guide.

For more on Deno, see the official Deno documentation.