JavaScript Console Emulator Free Online Tool 2026

Last updated March 22, 2026

Example: Array Methods

const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

// Filter even numbers
numbers.filter(n => n % 2 === 0)
// → [2, 4, 6, 8, 10]

// Map to squares
numbers.map(n => n ** 2)
// → [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

// Reduce to sum
numbers.reduce((sum, n) => sum + n, 0)
// → 55

// Chain operations
numbers
  .filter(n => n % 2 === 0)
  .map(n => n * 10)
  .reduce((sum, n) => sum + n, 0)
// → 300

Example: Object Destructuring and Spread

const user = { name: 'Alice', age: 30, city: 'New York' };

// Destructuring
const { name, age } = user;
console.log(name, age);
// → Alice 30

// Spread to merge objects
const updatedUser = { ...user, age: 31, email: 'alice@example.com' };
console.log(updatedUser);
// → { name: 'Alice', age: 31, city: 'New York', email: 'alice@example.com' }

// Rest parameters
const { name: userName, ...rest } = user;
console.log(rest);
// → { age: 30, city: 'New York' }

Example: Promises and Async/Await

// Promise chain
Promise.resolve(42)
  .then(n => n * 2)
  .then(n => n + 10)
  .then(console.log);
// → 94

// Async function
async function fetchData() {
  const result = await Promise.resolve({ status: 'ok', data: [1, 2, 3] });
  return result.data.map(n => n * 2);
}

fetchData().then(console.log);
// → [2, 4, 6]

// Promise.all
Promise.all([
  Promise.resolve('first'),
  Promise.resolve('second'),
  Promise.resolve('third')
]).then(console.log);
// → ["first", "second", "third"]

Example: Closures

// Counter using closure
function makeCounter(start = 0) {
  let count = start;
  return {
    increment: () => ++count,
    decrement: () => --count,
    value: () => count
  };
}

const counter = makeCounter(10);
counter.increment(); // → 11
counter.increment(); // → 12
counter.decrement(); // → 11
counter.value();     // → 11

Example: Prototype and Classes

class Animal {
  constructor(name) {
    this.name = name;
  }
  speak() {
    return `${this.name} makes a sound.`;
  }
}

class Dog extends Animal {
  speak() {
    return `${this.name} barks.`;
  }
}

const d = new Dog('Rex');
d.speak();                    // → "Rex barks."
d instanceof Dog;             // → true
d instanceof Animal;          // → true
Object.getPrototypeOf(d) === Dog.prototype;  // → true

Example: console.table Output

const users = [
  { name: 'Alice', age: 30, role: 'admin' },
  { name: 'Bob',   age: 25, role: 'user' },
  { name: 'Carol', age: 35, role: 'user' }
];

console.table(users);

// Output:
// ┌─────────┬─────────┬─────┬─────────┐
// │ (index) │  name   │ age │  role   │
// ├─────────┼─────────┼─────┼─────────┤
// │    0    │ 'Alice' │ 30  │ 'admin' │
// │    1    │  'Bob'  │ 25  │ 'user'  │
// │    2    │ 'Carol' │ 35  │ 'user'  │
// └─────────┴─────────┴─────┴─────────┘

Example: Error Handling

// Try/catch
try {
  JSON.parse('{ invalid json }');
} catch (e) {
  console.error('Parse error:', e.message);
}
// → Parse error: Unexpected token i in JSON at position 2

// Custom error
class ValidationError extends Error {
  constructor(field, message) {
    super(message);
    this.name = 'ValidationError';
    this.field = field;
  }
}

try {
  throw new ValidationError('email', 'Invalid email format');
} catch (e) {
  console.log(e.name, e.field, e.message);
}
// → ValidationError email Invalid email format

Example: Generator Functions

function* range(start, end, step = 1) {
  for (let i = start; i < end; i += step) {
    yield i;
  }
}

[...range(0, 10, 2)]
// → [0, 2, 4, 6, 8]

function* fibonacci() {
  let [a, b] = [0, 1];
  while (true) {
    yield a;
    [a, b] = [b, a + b];
  }
}

const fib = fibonacci();
Array.from({ length: 8 }, () => fib.next().value)
// → [0, 1, 1, 2, 3, 5, 8, 13]

Example: Regular Expressions

const text = 'Contact us at support@example.com or sales@company.org';

// Find all emails
const emails = text.match(/[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}/g);
console.log(emails);
// → ["support@example.com", "sales@company.org"]

// Replace with named groups
'2024-01-15'.replace(
  /(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})/,
  '$<day>/$<month>/$<year>'
);
// → "15/01/2024"

Type any JavaScript directly into the emulator and press Run to see the output immediately. No installation, no setup — just open the tool and start coding.

// Arithmetic
2 + 2          // → 4
10 / 3         // → 3.3333333333333335
2 ** 10        // → 1024
Math.sqrt(144) // → 12

// String operations
'Hello'.toUpperCase()           // → "HELLO"
'  trim me  '.trim()            // → "trim me"
'a,b,c'.split(',')              // → ["a", "b", "c"]
[1, 2, 3].join(' - ')           // → "1 - 2 - 3"