JavaScript Function Parameters

• Function parameters are variables listed as a part of a function declaration.
• They represent the values that a function expects to receive when it is called.

Syntax:

function functionName(parameter1, parameter2, /* ... */) {
  // Code to be executed when the function is called
}

parameter1, parameter2, ...: The parameters that the function accepts. They act as local variables within the function.

Why it is Used:

• Input Handling: Allows functions to receive input values or data for processing.
• Flexibility: Provides flexibility for the same function to work with different data.
• Modularity: Enables the creation of general-purpose functions that can be reused with varying inputs.

Example:

// Function Declaration with Parameters
function greet(name) {
  console.log('Hello, ' + name + '!');
}

// Calling the Function with Arguments
greet('John'); // Output: Hello, John!
greet('Alice'); // Output: Hello, Alice!

Default Parameters:

• You can provide default values for parameters using the assignment operator (=).
• Default parameters are used if a value is not explicitly provided when calling the function.

// Function Declaration with Default Parameter
function greet(name = 'Guest') {
  console.log('Hello, ' + name + '!');
}

// Calling the Function
greet(); // Output: Hello, Guest!
greet('Bob'); // Output: Hello, Bob!

Rest Parameters: The rest parameter syntax (...) allows a function to accept an arbitrary number of arguments as an array.

// Function Declaration with Rest Parameter
function sum(...numbers) {
  return numbers.reduce((acc, num) => acc + num, 0);
}

// Calling the Function
console.log(sum(1, 2, 3, 4)); // Output: 10

 

Summary

• Function parameters allow functions to receive input values.
• Default parameters provide fallback values if arguments are not provided.
• Rest parameters allow functions to accept an arbitrary number of arguments as an array.
• Proper use of parameters enhances the flexibility and reusability of functions in JavaScript.