Parameters and Arguments in JavaScript

When working with JavaScript functions, you will often hear two terms: parameters and arguments.

They are closely related, but they have different meanings.

What is a Parameter?

A parameter is a variable that we define inside the function's parentheses when creating a function.

It acts as a placeholder for the value that the function will receive.

Example

function greet(name) {
    console.log("Hello " + name);
}

Here, name is a parameter.

We haven't given name an actual value yet. It is simply waiting to receive a value.

function greet(name)
              ↑
          Parameter

What is an Argument?

An argument is the actual value that we pass to a function when calling it.

Example

greet("Abishek");

Here, "Abishek" is an argument.

The argument "Abishek" is passed to the parameter name.

greet("Abishek")
      ↑
    Argument

So, when the function runs:

function greet(name) {
    console.log("Hello " + name);
}

greet("Abishek");

The value "Abishek" is assigned to the parameter name.

Output:

Hello Abishek

---

Parameter vs Argument

Parameter	Argument
Defined in the function definition	Passed during function call
Acts as a placeholder	Contains the actual value
Example: name	Example: "Abishek"
Receives the value	Gives the value

Simple Example

function add(a, b) {
    console.log(a + b);
}

add(10, 20);

Here:

• a → Parameter
• b → Parameter
• 10 → Argument
• 20 → Argument

The flow is:

        Function Definition

        function add(a, b)
                     ↑  ↑
               Parameters


        Function Call

        add(10, 20)
            ↑   ↑
         Arguments

The values are passed like this:

a ← 10
b ← 20

Therefore:

10 + 20 = 30

Output:

30

---

Example with Multiple Arguments

A function can have multiple parameters and arguments.

function introduce(name, age, city) {
    console.log(name);
    console.log(age);
    console.log(city);
}

introduce("Abishek", 22, "Chennai");

Parameters

name
age
city

Arguments

"Abishek"
22
"Chennai"

The values are matched based on their position:

name ← "Abishek"
age  ← 22
city ← "Chennai"

---

What Happens If We Don't Pass an Argument?

If a parameter doesn't receive a value, JavaScript gives it the value undefined.

function greet(name) {
    console.log(name);
}

greet();

Output:

undefined

Because we called the function without passing an argument.

---

Default Parameters

We can also provide a default value for a parameter.

function greet(name = "Guest") {
    console.log("Hello " + name);
}

greet();

Output:

Hello Guest

Here, if no argument is passed, "Guest" is used as the default value.

If we pass an argument:

greet("Abishek");

Output:

Hello Abishek

The passed argument replaces the default value.

Final Summary

Parameter
   ↓
Placeholder defined in function

Argument
   ↓
Actual value passed during function call