Parameter Functions

Last Updated: 21st October 2025

A parameterized function is a function that takes input values as parameters and performs an action based on those values.It can be following types: Arguments are actual values passed when the function is called.

Parameterized function

Takes one or more parameters.

📝 Syntax:

function functionName(parameter1, parameter2, ...) {
    // code block
    //..
}

functionName(value1, value2, ...);

Example 1:

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

console.log(add(2, 3)); // 5

Example 2:

const greet = function (name) {
  console.log("Hello, " + name + "!");
};

greet("Sadhu"); // Output: "Hello, Sadhu!"

Example 3:

const sum = (a, b) => {
  console.log(a + b);
};

sum(2, 3); // Output: 5

// One-line return (implicit return)
const add = (a, b) => a + b;

// Single parameter (no need for parentheses)
const square = (n) => n * n;

Default parameters

A default parameter is a parameter that has a default value if no value is provided when the function is called.

📝 Syntax:

function functionName(parameter1, parameter2 = defaultValue) {
    // code block
    //..
}

Example:

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

greet(); // Output: "Hello, Guest!"
greet("Sadhu"); // Output: "Hello, Sadhu!"

Rest parameters

A rest parameter is a parameter that collects all the remaining arguments into an array.Used when number of arguments is unknown (... rest operator).

📝 Syntax:

function functionName(parameter1, parameter2, ..., parameterN) {
    // code block
    //..
}

Example:

function sum(...numbers) {
  let total = 0;
  for (const num of numbers) {
    total += num;
  }
  console.log(total);
}

sum(1, 2, 3, 4, 5); // Output: 15

💡 Quick Practice

  • Create a function add that takes two numbers and prints their sum.
  • Store a function in a variable add that adds two numbers.
  • Write an arrow function sub to subtract two numbers.
  • Try using this inside an arrow function and see the behavior.
  • Exercise Set 1
  • Exercise Set 2
← PreviousNext →