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Defining and Calling Functions

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Functions are one of the fundamental building blocks in JavaScript. A function is a reusable block of code designed to perform a particular task. This section will cover how to define and call functions in JavaScript.

Table of Contents

  1. What is a Function?
  2. Defining a Function
  3. Calling a Function
  4. Function Examples
  5. Practical Exercises
  6. Summary

What is a Function?

A function in JavaScript is a set of statements that performs a task or calculates a value. Functions can take inputs (parameters) and return an output (return value).

Defining a Function

In JavaScript, you can define a function using the function keyword. The basic syntax is:

function functionName(parameters) {
    // Function body
    // Code to be executed
}

Example:

function greet() {
    console.log("Hello, World!");
}

In this example, greet is the name of the function, and it contains a single statement that logs "Hello, World!" to the console.

Parameters

Functions can accept parameters, which are values passed to the function when it is called.

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

Here, the greet function takes one parameter, name, and uses it to log a personalized greeting.

Calling a Function

To execute the code inside a function, you need to call it. You do this by using the function name followed by parentheses. If the function has parameters, you pass the arguments inside the parentheses.

Example:

greet(); // Output: Hello, World!
greet("Alice"); // Output: Hello, Alice!

Function Examples

Example 1: Function with No Parameters

function sayHello() {
    console.log("Hello!");
}

sayHello(); // Output: Hello!

Example 2: Function with Parameters

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

let result = add(5, 3);
console.log(result); // Output: 8

Example 3: Function with Return Value

function multiply(a, b) {
    return a * b;
}

let product = multiply(4, 7);
console.log(product); // Output: 28

Practical Exercises

Exercise 1: Create a Function to Subtract Two Numbers

  1. Define a function named subtract that takes two parameters, a and b.
  2. The function should return the result of a - b.
  3. Call the function with the arguments 10 and 4, and log the result.
function subtract(a, b) {
    return a - b;
}

let difference = subtract(10, 4);
console.log(difference); // Output: 6

Exercise 2: Create a Function to Concatenate Strings

  1. Define a function named concatenate that takes two parameters, str1 and str2.
  2. The function should return the concatenation of str1 and str2.
  3. Call the function with the arguments "Hello, " and "World!", and log the result.
function concatenate(str1, str2) {
    return str1 + str2;
}

let message = concatenate("Hello, ", "World!");
console.log(message); // Output: Hello, World!

Summary

In this section, you learned how to define and call functions in JavaScript. Functions are essential for organizing and reusing code. You also practiced creating functions with and without parameters, as well as functions that return values. Understanding how to work with functions is crucial for writing efficient and maintainable JavaScript code.

Next, we will explore function expressions and arrow functions, which provide more ways to define functions in JavaScript.

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JavaScript: From Beginner to Advanced

Module 1: Introduction to JavaScript

Module 2: Control Structures

Module 3: Functions

Module 4: Objects and Arrays

Module 5: Advanced Objects and Functions

Module 6: The Document Object Model (DOM)

Module 7: Browser APIs and Advanced Topics

Module 8: Testing and Debugging

Module 9: Performance and Optimization

Module 10: JavaScript Frameworks and Libraries

Module 11: Final Project

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