arguments

Inside a non‑arrow function, the arguments object is an array‑like object containing the arguments passed to the function. It provides access to all arguments regardless of the function’s parameter list. However, it is not a true array; you must convert it if you need array methods.

Key Points

• Available only in traditional functions (not arrow functions).
• Has length property and indexed elements.
• Can be used to create variadic functions (accepting any number of arguments).
• In modern JavaScript, rest parameters (...args) are preferred over arguments.

Code Example

function sum() {
  console.log(arguments.length); // number of arguments
  console.log(arguments[0]); // first argument

  // Convert to array to use reduce
  const argsArray = Array.from(arguments);
  const total = argsArray.reduce((acc, val) => acc + val, 0);
  return total;
}

console.log(sum(1, 2, 3)); // 6

// Rest parameters (modern alternative)
function sumModern(...numbers) {
  return numbers.reduce((acc, val) => acc + val, 0);
}
console.log(sumModern(1, 2, 3)); // 6