What is arguments Pseudo-array in JavaScript

arguments is a built-in object available inside functions, containing all arguments passed to the function, regardless of whether they were explicitly declared in the signature.

It exists only in regular (not arrow) functions and allows working with a variable number of arguments.

Usage Example

function sum() {
  console.log(arguments); // Pseudo-array
  let total = 0;

  for (let i = 0; i < arguments.length; i++) {
    total += arguments[i];
  }

  return total;
}

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

arguments Object Features

Why is it a Pseudo-array?

It's similar to an array because:

• has indices
• has length

But:

• it's not a real Array
• doesn't have map, forEach, filter methods, etc.

Converting to Array

const args = Array.from(arguments);
// or
const args2 = [...arguments]; // only works in regular function

In Arrow Functions

const foo = () => {
  console.log(arguments); // ❌ ReferenceError
};

foo(1, 2, 3);

arguments doesn't exist in arrow functions because arrow functions don't create their own context.

Modern Alternative — Rest Parameters

function sum(...args) {
  return args.reduce((acc, curr) => acc + curr, 0);
}