Online JavaScript Compiler

Write, run, and debug JavaScript code right in the browser—perfect for learning, practice, and quick validation.

JavaScript Code Editor

Output

Standard Output (stdout)

 
  
 
Standard Error (stderr)
 
 
   
 
 
  
 
How to Use
 
     
  • Write JavaScript code in the left editor (modern ES syntax supported).
    •  
  • Click Run Code to execute instantly in a Node.js environment.
    •  
  • The right panel displays output and error messages.
    •  
  • The green area shows standard output (for example, console.log).
    •  
  • The red area highlights runtime errors and warnings.
    •  
  • Execution details include the exit code and runtime status.
    •  
  • Shortcut: Ctrl+Enter (use Cmd+Enter on macOS).
    •  
 
  
  
 
JavaScript Basics
 
 
 
Hello World:
 

console.log('Hello, JavaScript!');

 
 
 
Common Types:
 
     
  • number / string / boolean / null / undefined
    •  
  • object (including arrays []), function, symbol, bigint
    •  
  • Declare variables with const / let (block scope; avoid issues caused by var)
    •  
 
 
 
  
 
Control Flow
 
 
 
Conditionals and Loops:
 

const n = 5;

if (n % 2 === 0) {

  console.log('even');

} else {

  console.log('odd');

}

for (let i = 0; i < 3; i++) {

  console.log(i);

}

 
 
 
  
 
Functions and Arrays
 
 
 
Example:
 

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

const nums = [3, 7, 1, 9, 4];

console.log(add(2, 3));

console.log(Math.max(...nums));

 
 
 
 
  
 
Sample Programs (click Run above)
 
 
 
1. Recursive Factorial
 

function factorial(n) {

  return n <= 1 ? 1 : n * factorial(n - 1);

}

console.log('5! =', factorial(5));

 
 
 
2. Array Maximum
 

const nums = [3, 7, 1, 9, 4];

console.log('Maximum:', Math.max(...nums));