Thearguments object is a local variable available within all non-arrow functions. You can refer to a function's arguments inside that function by using itsarguments object. It has entries for each argument the function was called with, with the first entry's index at0.

For example, if a function is passed 3 arguments, you can access them as follows:

arguments[0]; // first argumentarguments[1]; // second argumentarguments[2]; // third argument

Thearguments object is useful for functions called with more arguments than they are formally declared to accept, calledvariadic functions, such asMath.min(). This example function accepts any number of string arguments and returns the longest one:

function longestString() {  let longest = "";  if (arguments.length === 0) {    throw new TypeError("At least one string is required");  }  for (const arg of arguments) {    if (arg.length > longest.length) {      longest = arg;    }  }  return longest;}

You can usearguments.length to count how many arguments the function was called with. If you instead want to count how many parameters a function is declared to accept, inspect that function'slength property.

Each argument index can also be set or reassigned:

arguments[1] = "new value";

Non-strict functions that only have simple parameters (that is, no rest, default, or destructured parameters) will sync the new value of parameters with thearguments object, and vice versa:

function func(a) {  arguments[0] = 99; // updating arguments[0] also updates a  console.log(a);}func(10); // 99function func2(a) {  a = 99; // updating a also updates arguments[0]  console.log(arguments[0]);}func2(10); // 99

Non-strict functions thatare passedrest,default, ordestructured parameters will not sync new values assigned to parameters in the function body with thearguments object. Instead, thearguments object in non-strict functions with complex parameters will always reflect the values passed to the function when the function was called.

function funcWithDefault(a = 55) {  arguments[0] = 99; // updating arguments[0] does not also update a  console.log(a);}funcWithDefault(10); // 10function funcWithDefault2(a = 55) {  a = 99; // updating a does not also update arguments[0]  console.log(arguments[0]);}funcWithDefault2(10); // 10// An untracked default parameterfunction funcWithDefault3(a = 55) {  console.log(arguments[0]);  console.log(arguments.length);}funcWithDefault3(); // undefined; 0

This is the same behavior exhibited by allstrict-mode functions, regardless of the type of parameters they are passed. That is, assigning new values to parameters in the body of the function never affects thearguments object, nor will assigning new values to thearguments indices affect the value of parameters, even when the function only has simple parameters.

arguments is an array-like object, which means thatarguments has alength property and properties indexed from zero, but it doesn't haveArray's built-in methods likeforEach() ormap(). However, it can be converted to a realArray, using one ofslice(),Array.from(), orspread syntax.

const args = Array.prototype.slice.call(arguments);// orconst args = Array.from(arguments);// orconst args = [...arguments];

For common use cases, using it as an array-like object is sufficient, since it bothis iterable and haslength and number indices. For example,Function.prototype.apply() accepts array-like objects.

function midpoint() {  return (    (Math.min.apply(null, arguments) + Math.max.apply(null, arguments)) / 2  );}console.log(midpoint(3, 1, 4, 1, 5)); // 3

arguments.calleeDeprecated

Reference to the currently executing function that the arguments belong to. Forbidden in strict mode.

arguments.length

The number of arguments that were passed to the function.

arguments[Symbol.iterator]()

Returns a newarray iterator object that contains the values for each index inarguments.

This example defines a function that concatenates several strings. The function's only formal argument is a string containing the characters that separate the items to concatenate.

function myConcat(separator) {  const args = Array.prototype.slice.call(arguments, 1);  return args.join(separator);}

You can pass as many arguments as you like to this function. It returns a string list using each argument in the list:

myConcat(", ", "red", "orange", "blue");// "red, orange, blue"myConcat("; ", "elephant", "giraffe", "lion", "cheetah");// "elephant; giraffe; lion; cheetah"myConcat(". ", "sage", "basil", "oregano", "pepper", "parsley");// "sage. basil. oregano. pepper. parsley"

This example defines a function that creates a string containing HTML for a list. The only formal argument for the function is a string that is"u" if the list is to beunordered (bulleted), or"o" if the list is to beordered (numbered). The function is defined as follows:

function list(type) {  let html = `<${type}l><li>`;  const args = Array.prototype.slice.call(arguments, 1);  html += args.join("</li><li>");  html += `</li></${type}l>`; // end list  return html;}

You can pass any number of arguments to this function, and it adds each argument as a list item to a list of the type indicated. For example:

list("u", "One", "Two", "Three");// "<ul><li>One</li><li>Two</li><li>Three</li></ul>"

Thetypeof operator returns'object' when used witharguments

console.log(typeof arguments); // 'object'

The type of individual arguments can be determined by indexingarguments:

console.log(typeof arguments[0]); // returns the type of the first argument

• Functions guide
• Functions
• Rest parameters