Online JavaScript & TypeScript Compiler — Numio

Run JavaScript and TypeScript online with modern ES2020+ syntax. See console.log output instantly in an isolated sandbox. Free, no sign-up.

Runs in your browser · No sign-up

const orders = [
  { id: 1, customer: "Ana", total: 42.5, paid: true },
  { id: 2, customer: "Ben", total: 18, paid: false },
  { id: 3, customer: "Ana", total: 27.25, paid: true }
];

class Cart {
  #items = [];
  add(name, price) {
    this.#items.push({ name, price });
    return this;
  }
  get total() {
    return this.#items.reduce((sum, item) => sum + item.price, 0);
  }
}

const wait = ms => new Promise(resolve => setTimeout(resolve, ms));

async function main() {
  const paid = orders.filter(order => order.paid);
  const spent = paid.reduce((sums, order) => {
    sums[order.customer] = (sums[order.customer] ?? 0) + order.total;
    return sums;
  }, {});
  console.log("Paid orders:", paid.map(order => order.id).join(", "));
  console.log("Spent per customer:", spent);

await wait(100);
  const cart = new Cart().add("Pen", 1.5).add("Notebook", 3.25);
  console.log(`Cart total: ${cart.total.toFixed(2)}`);

for (const { id, customer, total } of orders)
    console.log(`#${id}`.padEnd(4), customer.padEnd(5), total.toFixed(2).padStart(6));
}

main();

Ctrl/⌘ + Enter to run

Output

Code runs locally in your browser; it is not uploaded.

How to use

Choose JavaScript or TypeScript.
Write your code and print results with console.log.
Press Run (or Ctrl/⌘ + Enter) to see the output.

Example

// JavaScript example
const nums = [3, 1, 4, 1, 5, 9];
const sorted = [...nums].sort((a, b) => a - b);
console.log("Sorted:", sorted.join(", "));
console.log("Max:", Math.max(...nums));

Details and limitations

Code runs in QuickJS, a separate JavaScript engine compiled to WebAssembly. It is isolated from the page: no DOM, network or browser APIs.

TypeScript type annotations are removed before running. Type errors are not checked; only syntax errors are reported.

FAQ

Can I use document or fetch?

No. The sandbox has no DOM, network or browser APIs. To work with web pages, use the online HTML editor.

Does it check TypeScript types?

No. Types are stripped and the code runs as JavaScript, so only syntax errors are shown.

Which syntax is supported?

Modern JavaScript, including let/const, arrow functions, classes, destructuring, template literals and optional chaining.

Format references

Tool page updated: 2026-10-22