JS Puzzles · Const

arguments object

The arguments object is an array-like, iterable collection of every value supplied to a traditional function. It supports indexes and length, but not Array methods, and arrow functions inherit arguments from an enclosing normal function.

How it works

Inside a traditional function, arguments exposes every value supplied at the call site through numeric indexes and length. It is iterable and array-like, but it is not an Array, so convert it before using array methods. Arrow functions do not create their own arguments object.

Syntax

arguments

Key points

A traditional function can inspect every supplied argument through numeric indexes.
Use arguments.length to count how many values the caller supplied.
The object is iterable, so it can be traversed with for...of.
Treat arguments as array-like rather than as a true Array.
Convert arguments to an Array before calling Array methods.
It includes values even when the function declaration has fewer named parameters.

Common mistakes

arguments has indexes and length, but it does not provide Array methods such as map or reduce.
Arrow functions do not have their own arguments object; an arguments reference resolves to an enclosing normal function.
Unlike rest parameters, arguments cannot capture only a selected portion of the supplied values.

Example: Read all supplied arguments

function total() {
  return Array.from(arguments).reduce((sum, value) => sum + value, 0);
}

console.log(total(2, 3, 5)); // 10

Converts the array-like object to an array, then sums every supplied argument.

When to use it

Variadic functions

Accepting a variable number of values in legacy or interop code.

Argument counting

Inspecting how many values a caller supplied.

Dynamic argument processing

Iterating over caller-supplied values in a traditional function.

rest parameters
spread syntax
Array.from()
for...of

Source: Rest parameters and spread syntax. Checked 2026-10-15.