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Parameters & Arguments
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Functions are one of the most important building blocks in JavaScript. To make functions flexible and reusable, JavaScript provides parameters and arguments.

In this chapter, you will clearly understand:

  • What parameters are
  • What arguments are
  • The difference between them
  • How they work in real JavaScript programs


What Are Parameters in JavaScript?

Parameters are variables listed in a function definition. They act as placeholders that receive values when the function is called.


Example: Function with Parameters

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

Here:

  • name is a parameter
  • It does not have a value yet
  • It waits for input when the function is called
Think of parameters as empty boxes waiting to be filled.


What Are Arguments in JavaScript?

Arguments are the actual values passed to a function when it is invoked (called).


Example: Function Call with Arguments

greet("John");

Here:

  • "John" is an argument
  • It gets assigned to the parameter name
Arguments are real values, parameters are placeholders.


Difference Between Parameters and Arguments

ParametersArguments
Defined in functionPassed during functino call
Act as variablesAct as actual values
Used in funtion definitionUsed in function invocation


Function with Multiple Parameters

A function can have more than one parameter.


Example

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

add(5, 10);

Here:

  • a and b - parameters
  • 5 and 10 - arguments


Output

15


Order of Parameters and Arguments

Order matters in JavaScript


Example

function display(firstName, lastName) {
    console.log(firstName + " " + lastName);
}

display("Rahul", "Sharma");


Output

Rahul Sharma


If the order is changed

display("Sharma", "Rahul");


Output

Sharma Rahul

JavaScript assigns arguments based on position, not name.


Missing Arguments in JavaScript

If fewer arguments are passed than parameters, JavaScript assigns undefined.


Example

function showAge(age) {
    console.log(age);
}

showAge();


Output

undefined


Extra Arguments in JavaScript

If more arguments are passed than parameters, JavaScript ignores the extra ones.


Example

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

showName("Amit", 25, "India");


Output

Amit


Default Parameters (Modern JavaScript)

JavaScript allows you to set default values for parameters.


Example

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

greet();
greet("Neha");


Output

Hello Guest
Hello Neha

Default parameters prevent undefined values.


Why Parameters and Arguments Are Important

  • Make functions reusable
  • Allow dynamic input
  • Reduce code duplication
  • Improve readability and maintainability
Without parameters, functions would work only for fixed values.


Real World Use Case

function calculateTotal(price, quantity) {
    return price * quantity;
}

let total = calculateTotal(500, 2);
console.log(total);


Output

1000

This pattern is used everywhere: carts, forms, APIs, calculations.


Two Minute Drill

Parameters

  • Defined in the function declaration
  • Act as placeholders
  • Receive values when the function is called

Arguments

  • Passed during function invocation
  • Are actual values
  • Assigned based on position