Online JavaScript Editor.

Starter snippet

export function normalizeRows(rows) {
  return rows.map((row) => ({
    id: String(row.id ?? ''),
    active: Boolean(row.active),
  }));
}

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 limit = 10; let cursor = 0;

Loops

for (const item of list) { }  items.forEach(fn)

Functions / methods

function add(a, b) { return a + b; }

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

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

Error handling wrapper

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

Does code execute in the browser?

Execution is not bundled with this page—use it to edit, format where supported, and download.