Online TypeScript Editor

Starter snippet

type User = { id: string; roles: readonly string[] };

function hasRole(user: User, role: string): boolean {
  return user.roles.includes(role);
}

Fetch + JSON guard

export async function getJson(url) {
  const res = await fetch(url, { headers: { Accept: 'application/json' } });
  if (!res.ok) throw new Error(`HTTP ${res.status}`);
  return res.json();
}

Immutable update

const next = {
  ...state,
  items: state.items.map((it) =>
    it.id === id ? { ...it, done: true } : it
  ),
};

Variables

const port = 3000; let cache: Map<string, User> = new Map();

Loops

for (const [k, v] of cache) { }

Functions / methods

function pick<T, K extends keyof T>(obj: T, key: K): T[K] { return obj[key]; }

Comments

// line  /* block */

Bindings

const limit = 25;
let cursor = 0;
var legacy = true; // avoid in new code

Loops

for (const item of list) {
  work(item);
}

while (cursor < limit) { cursor++; }

Parse → transform → emit

// TypeScript pipeline sketch
const input = readLines();
const output = input
  .map(line => line.trim())
  .filter(Boolean)
  .map(transform);
writeLines(output);

Error handling wrapper

// TypeScript
function runSafely(task) {
  try {
    return { ok: true, value: task() };
  } catch (err) {
    return { ok: false, error: String(err) };
  }
}

Is TypeScript compiled here?

You edit TypeScript with syntax support; compilation happens in your project toolchain.