What are Parameters, Arguments and Arguments Object in JavaScript

In JavaScript, the terms parameters and arguments of a function are often used interchangeably. But there exists some difference between them. Let us see what they are with examples.

We are discussing the following things in this article

• What are parameters
• What are arguments
• What is an argument object?

What are parameters

Function parameters are the variables listed in the function definition. Let's take an example below:

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

Here, “a” and “b” are parameters in the “getSum()” function. Multiple parameters can be added inside parentheses, separated by commas.

What are Arguments

Arguments are values passed to the function when it is invoked.

function getSum(a, b){
return a+b;
}
var sum = getSum(1, 2);

In the above example ‘1’ and ‘2’ are the arguments passed to the “getSum” function. 

What is an Arguments Object

The arguments object is an object which is a local variable available with all functions by default except arrow functions in JavaScript.

function getSum(a, b){
    console.log(arguments[0]);
    // expected output: 1

    console.log(arguments[1]);
    // expected output: 2
}
var sum = getSum(1, 2);

This object (arguments) is used to access the values passed to a function. It is only available within a function and can’t access from the outside. The arguments object allows you to access all of the arguments that are passed to that function as in the above example. It is not an array but, we can access elements using the index starting from 0, and it has a length property that contains the number of arguments passed to the function.

The arguments objects contain all of the arguments passed during the function call, even if there are not as many parameters in the function declaration. Look at the below example:

function calculate() {
   console.log(arguments[3]);
   // print 5 in the console

   console.log(arguments[4]);
   // print undefined in the console
}
calculate(1,2,3,5);  

The output of the console.log(arguments[4]);  is undefined because we are passing only four arguments to function calculate( ) which would be located at the 0 to 3rd index. But here we are accessing arguments[4] which is not available. So it is giving output as undefined.