Run JavaScript & Node.js Online

Use a real-time CLI to execute JS/Node.js code directly in your browser—great for testing logic and modules.

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Sample

🚀 319,634 total executions (750 this month)

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⚡ About This JavaScript (Node.js) Online Executor

The CodeUtility JavaScript Executor lets you write and run modern JavaScript code right in your browser - instantly and without any setup. It uses real Node.js environments to execute your code securely in a sandboxed container, supporting versions 16, 18, and 20.

This tool is perfect for testing Node.js snippets, exploring ES6+ syntax, or learning core JavaScript programming concepts such as loops, functions, arrays, promises, and async/await behavior.

You can also use it to validate algorithms, debug small scripts, or experiment with runtime logic without installing Node locally. It’s ideal for learners, backend developers, or anyone who needs a fast, browser-based way to run JavaScript code.

💡 How to Use This Tool

1. Choose a Node.js version from the dropdown above the editor (16, 18, or 20).
2. Write or paste your JavaScript code directly into the editor.
3. Click Run to execute your code and view the output instantly in the console below.
4. While running, a Stop button appears - click it to terminate execution early.
5. Use Fix Code to automatically fix common syntax or indentation errors.
6. After fixing, a Fixes button appears - click it to review your recent corrections.
7. You can also Upload a local file or Download your current script from the editor.
8. Each run is limited to 20 seconds for efficiency and fair use across all users.

🧠 Tip: The Node.js runtime supports modern ECMAScript features - perfect for testing async code, modules, and JSON parsing in real time.

💡 Node.js Basics Guide for Beginners

1. Declaring Variables and Constants

Use let or const for block-scoped variables. const is used for constants.

let x = 10;
const PI = 3.14;
let name = "Alice";
let isActive = true;

2. Conditionals (if / switch)

Use if, else if, else or switch for control flow.

let x = 2;
if (x === 1) {
  console.log("One");
} else if (x === 2) {
  console.log("Two");
} else {
  console.log("Other");
}

switch (x) {
  case 1:
    console.log("One");
    break;
  case 2:
    console.log("Two");
    break;
  default:
    console.log("Other");
}

3. Loops

Use for, while, and forEach to iterate over data.

for (let i = 0; i < 3; i++) {
  console.log(i);
}

let n = 3;
while (n > 0) {
  console.log(n);
  n--;
}

4. Arrays

Use arrays to store ordered lists of values. Access them with indexes.

let fruits = ["apple", "banana", "cherry"];
console.log(fruits[0]);
console.log(fruits.length);

5. Array Manipulation

Use methods like push, pop, slice, and reverse.

fruits.push("kiwi");
fruits.pop();
console.log(fruits.slice(0, 2));
console.log(fruits.reverse());

let squares = [1, 2, 3, 4, 5].map(x => x * x);
console.log(squares);

6. Console Input/Output

Use console.log for output and readline module for input.

const readline = require('readline');

const rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout
});

rl.question("What's your name? ", name => {
  console.log(`Hello, ${name}`);
  rl.close();
});

7. Functions

Functions can be declared or expressed. Arrow functions are often used in modern JavaScript.

function greet(name) {
  return `Hello, ${name}`;
}

const add = (a, b) => a + b;

console.log(greet("Alice"));
console.log(add(2, 3));

8. Objects (Maps)

Objects store key-value pairs. They are similar to dictionaries or maps.

let person = { name: "Bob", age: 25 };
console.log(person.name);
console.log(person["age"]);

// ES6 Map
const map = new Map();
map.set("a", 1);
console.log(map.get("a"));

9. Exception Handling

Use try, catch, and finally to handle errors safely.

try {
  throw new Error("Something went wrong");
} catch (e) {
  console.log(e.message);
} finally {
  console.log("Cleanup if needed");
}

10. File I/O

Use Node.js's fs module to read and write files.

const fs = require("fs");

fs.writeFileSync("test.txt", "Hello File");
const data = fs.readFileSync("test.txt", "utf8");
console.log(data);

11. String Manipulation

Use methods like trim(), toUpperCase(), replace(), and split().

let text = "  Hello World  ";
console.log(text.trim());
console.log(text.toUpperCase());
console.log(text.replace("Hello", "Hi"));
console.log(text.split(" "));

12. Classes & Objects

ES6+ supports OOP with class syntax.

class Person {
  constructor(name) {
    this.name = name;
  }
  greet() {
    return `Hi, I'm ${this.name}`;
  }
}

const p = new Person("Alice");
console.log(p.greet());

13. References

Objects and arrays in JavaScript are passed by reference.

function update(arr) {
  arr.push("changed");
}

let data = ["original"];
update(data);
console.log(data);  // ["original", "changed"]