JavaScript User Defined Functions – Learn and Practice

JavaScript User Defined Functions 

Explore the world of -defined functions in JavaScript. Learn how to create, use, and optimize custom functions for modularity and code reusability.”

In JavaScript, functions are blocks of reusable code that can be defined by the  to perform specific tasks. Here’s a basic overview of how to create and use -defined functions in JavaScript:

JavaScript Function Declaration:

You can define a function using the function keyword followed by the function name, a list of parameters enclosed in parentheses, and the function body enclosed in curly braces.

Here’s an example:

javascript

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

Function Expression:

Functions can also be defined using function expressions, where you assign an anonymous function to a variable. This allows you to pass functions as arguments to other functions or store them in variables. Here’s an example:

javascript

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

JavaScript Arrow Functions (ES6):

Arrow functions are a concise way to define functions introduced in ECMAScript 2015 (ES6).

They have a shorter syntax and automatically bind to the enclosing context.

Here’s an example:

javascript

const multiply = (a, b) => a * b;

Calling Functions:

Once you’ve defined a function, you can call it by using its name followed by parentheses containing the arguments you want to pass to the function. Here’s how you can call the previously defined functions:

javascript

greet("Gogo");       // Outputs: Hello, Gogo!
console.log(add(5, 3)); // Outputs: 8
console.log(multiply(4, 6)); // Outputs: 24

Return Statements:

Functions can return values using the return statement. When a return statement is encountered, the function stops executing and the specified value is returned to the caller. Here’s an example:

javascript

function subtract(a, b) {
    return a - b;
}

Document.write.(subtract(10, 4)); // Outputs: 6

Remember that functions in JavaScript are first-class citizens, meaning they can be assigned to variables, passed as arguments to other functions, and returned as values from other functions.

-defined functions are a fundamental concept in JavaScript programming, allowing you to organize your code into reusable chunks and make your code more modular and maintainable.

step by step how to create  function

Here’s a step-by-step guide on how to create a -defined function in JavaScript:

Step 1: Decide on the Function’s Purpose

Before you create a function, you should have a clear understanding of what task or calculation the function will perform. Identify the input (parameters) the function will need and the output (return value) it should provide.

Step 2: Choose a Function Name

Choose a descriptive and meaningful name for your function that reflects its purpose. Function names are identifiers and should follow JavaScript naming conventions (camelCase is commonly used).

Step 3: Declare the Function

There are different ways to declare functions in JavaScript. Choose the appropriate method based on your needs:

Function Declaration:

javascript

function functionName(parameter1, parameter2) {
    // Function body: code that performs the desired task
    // You can use the parameters and perform operations here
    return result; // Optional: if the function should return a value
}
Function Expression:
javascript
const functionName = function(parameter1, parameter2) {
    // Function body
    return result;
};
Arrow Function (ES6):
javascript
const functionName = (parameter1, parameter2) => {
    // Function body
    return result;
};

Step 4: Write the Function Body

Inside the function body, write the code that performs the desired task using the provided parameters. You can perform calculations, manipulate data, or execute any other logic necessary.

javascript

function addNumbers(a, b) {
    const sum = a + b;
    return sum;
}

Step 5: Return a Value (Optional)

If your function is meant to provide a result, use the return statement to send that result back to the caller. If your function doesn’t need to return anything, you can omit the return statement.

Step 6: Call the Function

To use the function you’ve defined, call it by its name followed by parentheses containing the required arguments. Capture the returned value, if any.

javascript

const result = addNumbers(5, 3);
console.log(result); // Outputs: 8

That’s it! You’ve successfully created a -defined function in JavaScript. You can now reuse this function throughout your code to perform the specific task it was designed for.

Remember that functions can be as simple or as complex as needed, and they play a crucial role in organizing your code, improving readability, and promoting code reusability.

Complete code example in html

Here’s a complete example of using a -defined function in an HTML document:

<!DOCTYPE html>
<html>
<head>
    <title>Function Example</title>
</head>
<body>
    <h1>Function Example</h1>
    <script>
        // Define a -defined function
        function addNumbers(a, b) {
            const sum = a + b;
            return sum;
        }
        // Call the function and display the result
        const result = addNumbers(5, 3);
        document.write("The result of adding 5 and 3 is: " + result);
    </script>
</body>
</html>

In this example:

1. The HTML document includes a <script> tag where you can write JavaScript code.
2. Inside the <script> tag, we define a -defined function addNumbers that takes two parameters a and b and returns their sum.
3. We then call the addNumbers function with the arguments 5 and 3 and store the result in the result variable.
4. We use the document.write() method to display the result in the web page.
5. When you open this HTML file in a web browser, you’ll see the text “The result of adding 5 and 3 is: 8” displayed on the page. This example demonstrates how to define, call, and use a -defined function within an HTML document.

Here’s another example that demonstrates a -defined function for calculating the area of a rectangle. The function will take the width and height of the rectangle as parameters and return the calculated area. This example also includes a simple HTML form to input the dimensions and display the result.

<!DOCTYPE html>
<html>
<head>
    <title>Rectangle Area Calculator</title>
</head>
<body>
    <h1>Rectangle Area Calculator</h1>
    <form id="rectangleForm">
        <label for="width">Width:</label>
        <input type="number" id="width" name="width" required><br><br>
        <label for="height">Height:</label>
        <input type="number" id="height" name="height" required><br><br>

        <button type="button" onclick="calculateArea()">Calculate Area</button>
    </form>
    <p id="result"></p>
    <script>
        // -defined function to calculate rectangle area
        function calculateArea() {
            const width = parseFloat(document.getElementById("width").value);
            const height = parseFloat(document.getElementById("height").value);
            if (!isNaN(width) && !isNaN(height)) {
                const area = width * height;
                document.getElementById("result").textContent = "The area of the rectangle is: " + area;
            } else {
                document.getElementById("result").textContent = "Please enter valid dimensions.";
            }
        }
    </script>
</body>
</html>

In this example:

1. The HTML form includes input fields for width and height, and a button to trigger the calculation.
2. The calculateArea function reads the width and height values from the input fields and calculates the area.
3. The calculated area is then displayed in the paragraph element with the id “result”.
4. The parseFloat function is used to convert the input values to floating-point numbers for calculations.
5. The isNaN function is used to check if the input values are valid numbers.
6. When you enter valid numeric values for width and height and click the “Calculate Area” button, the area of the rectangle will be displayed below the form. If you enter non-numeric values or leave the fields empty, an appropriate message will be displayed instead.

Here’s another example that demonstrates a -defined function to check whether a given number is prime. This example will allow s to input a number and then show whether the number is prime or not using JavaScript.

<!DOCTYPE html>
<html>
<head>
    <title>Prime Number Checker</title>
</head>
<body>
    <h1>Prime Number Checker</h1>
    <form id="primeForm">
        <label for="number">Enter a number:</label>
        <input type="number" id="number" name="number" required><br><br>
        <button type="button" onclick="checkPrime()">Check Prime</button>
    </form>
    <p id="result"></p>

    <script>
        // -defined function to check if a number is prime
        function isPrime(num) {
            if (num <= 1) {
                return false;
            }
            for (let i = 2; i <= Math.sqrt(num); i++) {
                if (num % i === 0) {
                    return false;
                }
            }
            return true;
        }
        // Function to handle the prime number checking
        function checkPrime() {
            const num = parseInt(document.getElementById("number").value);
            if (!isNaN(num)) {
                const result = isPrime(num) ? "is prime" : "is not prime";
                document.getElementById("result").textContent = num + " " + result;
            } else {
                document.getElementById("result").textContent = "Please enter a valid number.";
            }
        }
    </script>
</body>
</html>

In this example:

1. The HTML form allows s to input a number and click the “Check Prime” button.
2. The isPrime function checks whether a given number is prime by iterating from 2 to the square root of the number and checking for divisibility.
3. The checkPrime function reads the input value, calls the isPrime function, and displays the result.
4. When you enter a number and click the “Check Prime” button, the page will indicate whether the entered number is prime or not. The result will be displayed below the form. If you enter a non-numeric value or leave the input field empty, an appropriate message will be shown.

Importance and uses of  function

-defined functions play a vital role in programming and offer several benefits and use cases. Here are some of the key importance and uses of -defined functions:

Modularity and Reusability:

 functions allow you to break down complex tasks into smaller, manageable parts. Each function can perform a specific task, making the code more modular and organized. Once a function is defined, it can be reused throughout your code, saving you time and effort.

Readability and Maintainability:

Functions enhance code readability by encapsulating logic within well-named blocks. This makes it easier for other developers (and your future self) to understand the code’s purpose and functionality. Additionally, changes or updates can be made to a specific function without affecting the rest of the codebase.

Abstraction and Encapsulation:

Functions allow you to abstract away the implementation details of a particular task. Other parts of the code only need to know how to call the function and interpret its result. This encapsulation hides the internal details, promoting separation of concerns.

Code Reusability:

Once you’ve written a function to perform a specific task, you can reuse it in multiple places without rewriting the same code. This reduces redundancy and helps maintain consistency across your application.

Parameterization:

Functions can accept parameters, allowing you to create flexible and customizable code. By passing different values as parameters, you can achieve variations of the same task without duplicating code.

Testing and Debugging:

Isolating specific functionality in functions makes it easier to test and debug your code. You can focus on testing individual functions independently, ensuring that they work as expected.

Collaboration:

In collaborative projects, using well-defined functions promotes collaboration among team members. Different team members can work on different parts of the codebase without stepping on each other’s toes.

Library Creation:

Functions are the building blocks of libraries and frameworks. By defining reusable functions, developers can create libraries that solve common problems and make them available to others.

Customization and Extension:

 functions can be extended or modified to fit specific requirements. As your project evolves, you can enhance or adapt existing functions to accommodate new features.

Performance Optimization:

Well-designed functions can lead to optimized code. By separating frequently executed code into functions, you can take advantage of performance optimization techniques such as memoization.

Overall, -defined functions are a cornerstone of modern programming. They promote code organization, reusability, and maintainability, which are critical aspects of writing efficient and scalable software applications.

Modularity and Reusability:complete code example in html

Here’s a complete HTML code example that demonstrates the concept of modularity and reusability through -defined functions. In this example, we’ll create two functions: one to calculate the area of a rectangle and another to calculate the volume of a box. These functions can be reused whenever needed.

<!DOCTYPE html>
<html>
<head>
    <title>Modularity and Reusability Example</title>
</head>
<body>
    <h1>Modularity and Reusability Example</h1>
    <script>
        // -defined function to calculate the area of a rectangle
        function calculateRectangleArea(width, height) {
            return width * height;
        }
        // -defined function to calculate the volume of a box
        function calculateBoxVolume(length, width, height) {
            return length * width * height;
        }
        // Calculate and display area and volume
        const rectangleWidth = 5;
        const rectangleHeight = 10;
        const rectangleArea = calculateRectangleArea(rectangleWidth, rectangleHeight);

        const boxLength = 3;
        const boxWidth = 4;
        const boxHeight = 6;
        const boxVolume = calculateBoxVolume(boxLength, boxWidth, boxHeight);
        document.write("Rectangle Area: " + rectangleArea + "<br>");
        document.write("Box Volume: " + boxVolume);
    </script>
</body>
</html>

In this example:

1. We defin
2. e two -defined functions: calculateRectangleArea and calculateBoxVolume.
3. Each function takes parameters representing the dimensions of the shape and returns the calculated area or volume.
4. We call these functions with specific values for width, height, length, and so on.
5. The calculated values are then displayed on the web page using the document.write() method.
6. When you open this HTML file in a web browser, you’ll see the calculated area of the rectangle and the volume of the box displayed on the page. This example demonstrates how -defined functions can encapsulate specific calculations, making them reusable throughout your code while promoting modularity and readability.

Readability and Maintainability:complete code example

Here’s a complete HTML code example that demonstrates how -defined functions improve readability and maintainability of your code. In this example, we’ll create a function to check if a given year is a leap year, and then we’ll use this function to determine if a set of years are leap years or not.

<!DOCTYPE html>
<html>
<head>
    <title>Readability and Maintainability Example</title>
</head>
<body>
    <h1>Readability and Maintainability Example</h1>
    <script>
        // -defined function to check if a year is a leap year
        function isLeapYear(year) {
            if ((year % 4 === 0 && year % 100 !== 0) || year % 400 === 0) {
                return true;
            } else {
                return false;
            }
        }
        // Array of years to check
        const yearsToCheck = [2000, 2020, 2100, 2024, 1900, 2022];
        // Check and display whether each year is a leap year
        for (const year of yearsToCheck) {
            const leapStatus = isLeapYear(year) ? "is" : "is not";
            document.write(year + " " + leapStatus + " a leap year.<br>");
        }
    </script>
</body>
</html>

In this example:

1. We define a -defined function called isLeapYear that takes a year as a parameter and returns true if it’s a leap year and false if it’s not.
2. We create an array yearsToCheck containing a list of years we want to check for leap year status.
3. We use a loop to iterate through the years in the array and call the isLeapYear function for each year.
4. The result is then displayed on the web page using the document.write() method.
5. When you open this HTML file in a web browser, you’ll see a list of years along with their leap year status. This example demonstrates how -defined functions improve the readability of code by encapsulating complex logic and promoting maintainability by centralizing the leap year calculation logic in a single function.

Abstraction and Encapsulation:complete code example

Here’s a complete HTML code example that illustrates abstraction and encapsulation using -defined functions. In this example, we’ll create a simple “Bank Account” abstraction, encapsulating the logic for depositing and withdrawing funds.

<!DOCTYPE html>
<html>
<head>
    <title>Abstraction and Encapsulation Example</title>
</head>
<body>
    <h1>Abstraction and Encapsulation Example</h1>

    <script>
        // -defined BankAccount class (abstraction)
        class BankAccount {
            constructor(initialBalance) {
                this.balance = initialBalance;
            }

            deposit(amount) {
                if (amount > 0) {
                    this.balance += amount;
                    return true;
                }
                return false;
            }

            withdraw(amount) {
                if (amount > 0 && amount <= this.balance) {
                    this.balance -= amount;
                    return true;
                }
                return false;
            }

            getBalance() {
                return this.balance;
            }
        }

        // Create a bank account object
        const myAccount = new BankAccount(1000);

        // Perform transactions and display balance
        myAccount.deposit(500);
        myAccount.withdraw(200);

        const currentBalance = myAccount.getBalance();
        document.write("Current Balance: $" + currentBalance);
    </script>
</body>
</html>

In this example:

1. We define a -defined class BankAccount to represent a bank account. This class encapsulates the logic for depositing, withdrawing, and checking the account balance.
2. The class’s methods (deposit, withdraw, and getBalance) abstract away the internal implementation details.
3. We create an instance of the BankAccount class called myAccount with an initial balance of $1000.
4. We perform a deposit of $500 and a withdrawal of $200 on the account.
5. Finally, we display the current balance on the web page using the document.write() method.
6. When you open this HTML file in a web browser, you’ll see the current balance of the bank account displayed on the page. This example demonstrates how -defined classes and methods can encapsulate complex functionality, providing an abstraction that hides implementation details and promotes code organization and reusability.

Code Reusability:complete code example

Of course! Here’s a compete HTML code example that demonstrates code reusability using -defined functions. In this example, we’ll create a function to calculate the factorial of a number and then reuse this function to calculate factorials for different numbers.

<!DOCTYPE html>
<html>
<head>
    <title>Code Reusability Example</title>
</head>
<body>
    <h1>Code Reusability Example</h1>

    <script>
        // -defined function to calculate the factorial of a number
        function calculateFactorial(number) {
            if (number === 0 || number === 1) {
                return 1;
            }
            return number * calculateFactorial(number - 1);
        }

        // Calculate and display factorials for different numbers
        const numbersToCalculate = [5, 3, 7, 0, 10];

        for (const number of numbersToCalculate) {
            const factorial = calculateFactorial(number);
            document.write("Factorial of " + number + ": " + factorial + "<br>");
        }
    </script>
</body>
</html>

In this example:

1. We define a -defined function called calculateFactorial that uses recursion to calculate the factorial of a given number.
2. We create an array numbersToCalculate containing the numbers for which we want to calculate factorials.
3. We use a loop to iterate through the numbers in the array and call the calculateFactorial function for each number.
4. The calculated factorials are then displayed on the web page using the document.write() method.
5. When you open this HTML file in a web browser, you’ll see a list of factorials for the numbers specified in the array. This example demonstrates how -defined functions enhance code reusability by allowing you to perform the same operation (calculating factorials) on different values without duplicating the logic.

Parameterization:complete code example

Absolutely! Here’s a complete HTML code example that showcases parameterization using -defined functions. In this example, we’ll create a function to generate a greeting message for a person’s name and customize the greeting by allowing the caller to provide a custom message prefix.

<!DOCTYPE html>
<html>
<head>
    <title>Parameterization Example</title>
</head>
<body>
    <h1>Parameterization Example</h1>

    <script>
        // -defined function to generate a customized greeting
        function generateGreeting(name, prefix = "Hello") {
            return prefix + ", " + name + "!";
        }

        // Generate and display greetings with different prefixes
        const personName = "Gogo";
        const greetings = [
            generateGreeting(personName),
            generateGreeting(personName, "Hi"),
            generateGreeting(personName, "Hey")
        ];

        for (const greeting of greetings) {
            document.write(greeting + "<br>");
        }
    </script>
</body>
</html>

In this example:

1. We define a -defined function called generateGreeting that takes a person’s name and an optional prefix as parameters. It combines the prefix, name, and exclamation mark to create a greeting message.
2. We create an array greetings containing different greetings with different prefixes for the same person’s name.
3. We use a loop to iterate through the greetings in the array and call the generateGreeting function with varying prefixes.
4. The generated greetings are then displayed on the web page using the document.write() method.
5. When you open this HTML file in a web browser, you’ll see a list of customized greetings for the person’s name “Gogo,” using different prefixes. This example demonstrates how -defined functions with parameterization allow you to create flexible and customizable code that can adapt to different scenarios without duplicating code logic.

Testing and Debugging:complete code example

Here’s a complete HTML code example that illustrates testing and debugging using -defined functions. In this example, we’ll create a function to find the largest number in an array of numbers and then test it with different arrays for debugging purposes.

<!DOCTYPE html>
<html>
<head>
    <title>Testing and Debugging Example</title>
</head>
<body>
    <h1>Testing and Debugging Example</h1>

    <script>
        // -defined function to find the largest number in an array
        function findLargestNumber(numbers) {
            if (numbers.length === 0) {
                return null; // Return null for an empty array
            }

            let largest = numbers[0];
            for (const number of numbers) {
                if (number > largest) {
                    largest = number;
                }
            }
            return largest;
        }

        // Test the function with different arrays for debugging
        const array1 = [5, 8, 2, 11, 3];
        const array2 = [20, 15, 30, 25];
        const array3 = [];

        const result1 = findLargestNumber(array1);
        const result2 = findLargestNumber(array2);
        const result3 = findLargestNumber(array3);

        document.write("Largest number in array1: " + result1 + "<br>");
        document.write("Largest number in array2: " + result2 + "<br>");
        document.write("Largest number in array3: " + result3 + "<br>");
    </script>
</body>
</html>

In this example:

1. We define a -defined function called findLargestNumber that takes an array of numbers as a parameter and returns the largest number in the array.
2. We test the function with different arrays (array1, array2, and array3) to verify its correctness and check how it handles different scenarios.
3. We use the document.write() method to display the largest numbers found in each array.
4. When you open this HTML file in a web browser, you’ll see the largest numbers in the different arrays displayed on the page. This example demonstrates how -defined functions facilitate testing and debugging by allowing you to isolate specific functionality for examination and validation.

Collaboration:complete code example

Here’s a complete HTML code example that showcases collaboration using -defined functions. In this example, we’ll create a function to calculate the area of a circle and then simulate a scenario where different team members use the same function in their respective parts of the code.

<!DOCTYPE html>
<html>
<head>
    <title>Collaboration Example</title>
</head>
<body>
    <h1>Collaboration Example</h1>
    <script>
        // -defined function to calculate the area of a circle
        function calculateCircleArea(radius) {
            return Math.PI * radius * radius;
        }

        // Developer A's code
        const radiusA = 5;
        const areaA = calculateCircleArea(radiusA);
        document.write("Developer A's Circle Area: " + areaA.toFixed(2) + "<br>");

        // Developer B's code
        const radiusB = 8;
        const areaB = calculateCircleArea(radiusB);
        document.write("Developer B's Circle Area: " + areaB.toFixed(2) + "<br>");
    </script>
</body>
</html>

In this example:

1. We define a -defined function called calculateCircleArea that takes the radius of a circle as a parameter and returns its area using the formula π * radius^2.
2. Developer A and Developer B use the same calculateCircleArea function in their respective parts of the code to calculate the areas of circles with different radii.
3. The calculated circle areas are displayed on the web page using the document.write() method.
4. When you open this HTML file in a web browser, you’ll see the calculated areas of circles for Developer A and Developer B displayed on the page. This example demonstrates how -defined functions facilitate collaboration among different team members, enabling them to use the same logic for calculations in their respective parts of the codebase.

Library Creation:complete code example

Here’s a complete HTML code example that illustrates library creation using -defined functions. In this example, we’ll create a simple utility library with functions to perform basic math operations and then use these functions in our code.

<!DOCTYPE html>
<html>
<head>
    <title>Library Creation Example</title>
</head>
<body>
    <h1>Library Creation Example</h1>
    <script>
        // -defined utility library
        const MathUtils = {
            add: function(a, b) {
                return a + b;
            },
            subtract: function(a, b) {
                return a - b;
            },
            multiply: function(a, b) {
                return a * b;
            },
            divide: function(a, b) {
                if (b !== 0) {
                    return a / b;
                } else {
                    return "Cannot divide by zero";
                }
            }
        };
        // Using functions from the utility library
        const num1 = 10;
        const num2 = 5;
        const sum = MathUtils.add(num1, num2);
        const difference = MathUtils.subtract(num1, num2);
        const product = MathUtils.multiply(num1, num2);
        const quotient = MathUtils.divide(num1, num2);
        document.write("Sum: " + sum + "<br>");
        document.write("Difference: " + difference + "<br>");
        document.write("Product: " + product + "<br>");
        document.write("Quotient: " + quotient + "<br>");
    </script>
</body>
</html>

In this example:

1. We define a -defined utility library MathUtils that contains functions for basic math operations such as addition, subtraction, multiplication, and division.
2. We use the functions from the utility library to perform calculations on num1 and num2.
3. The calculated results are displayed on the web page using the document.write() method.
4. When you open this HTML file in a web browser, you’ll see the results of various math operations performed using the functions from the MathUtils library. This example demonstrates how -defined functions can be organized into a library for reuse across different parts of your codebase.

Customization and Extension:complete code example

Here’s a complete HTML code example that demonstrates customization and extension using -defined functions. In this example, we’ll create a function to generate a message for a person’s name and customize the message based on  preferences.

<!DOCTYPE html>
<html>
<head>
    <title>Customization and Extension Example</title>
</head>
<body>
    <h1>Customization and Extension Example</h1>

    <script>
        // -defined function to generate a customized message
        function generateMessage(name, options = {}) {
            const defaultMessage = "Hello, " + name + "!";
            const greeting = options.greeting || "Hello";
            const punctuation = options.punctuation || "!";

            return greeting + ", " + name + punctuation;
        }

        // Generate and display customized messages
        const personName = "Bob";

        const defaultMessage = generateMessage(personName);
        document.write("Default Message: " + defaultMessage + "<br>");

        const friendlyMessage = generateMessage(personName, { greeting: "Hey", punctuation: " :)" });
        document.write("Friendly Message: " + friendlyMessage + "<br>");

        const formalMessage = generateMessage(personName, { greeting: "Good day", punctuation: "." });
        document.write("Formal Message: " + formalMessage + "<br>");
    </script>
</body>
</html>

In this example:

1. We define a -defined function called generateMessage that takes a person’s name and an options object as parameters. The options object allows s to customize the greeting and punctuation.
2. We provide default values for the greeting and punctuation using the options object.
3. We create different customized messages using the generateMessage function by passing different options.
4. The generated messages are displayed on the web page using the document.write() method.
5. When you open this HTML file in a web browser, you’ll see different customized messages for the person’s name “Bob,” using different greetings and punctuations. This example demonstrates how -defined functions can be customized and extended using optional parameters, allowing s to adapt the function’s behavior to their preferences.

Performance Optimization:complete code example

Here’s a complete HTML code example that illustrates performance optimization using -defined functions. In this example, we’ll create a function to calculate Fibonacci numbers using memoization to improve performance for large Fibonacci sequences.

<!DOCTYPE html>
<html>
<head>
    <title>Performance Optimization Example</title>
</head>
<body>
    <h1>Performance Optimization Example</h1>
    <script>
        // -defined function to calculate Fibonacci numbers using memoization
        const memo = {};

        function calculateFibonacciWithMemoization(n) {
            if (n in memo) {
                return memo[n];
            }

            if (n <= 1) {
                return n;
            }

            memo[n] = calculateFibonacciWithMemoization(n - 1) + calculateFibonacciWithMemoization(n - 2);
            return memo[n];
        }

        // Calculate and display Fibonacci numbers
        const fibonacciNumbersToCalculate = [10, 20, 30];

        for (const n of fibonacciNumbersToCalculate) {
            const fibonacciNumber = calculateFibonacciWithMemoization(n);
            document.write("Fibonacci(" + n + "): " + fibonacciNumber + "<br>");
        }
    </script>
</body>
</html>

In this example:

1. We define a -defined function called calculateFibonacciWithMemoization that calculates Fibonacci numbers using memoization to store already computed values and avoid redundant calculations.
2. The function stores calculated values in the memo object to optimize performance.
3. We create an array fibonacciNumbersToCalculate containing different values of n for which we want to calculate Fibonacci numbers.
4. We use a loop to iterate through the values of n and call the calculateFibonacciWithMemoization function to calculate the corresponding Fibonacci number.
5. The calculated Fibonacci numbers are then displayed on the web page using the document.write() method.
6. When you open this HTML file in a web browser, you’ll see the calculated Fibonacci numbers for the specified values of n. This example demonstrates how -defined functions can be optimized for performance using techniques like memoization to avoid redundant calculations and improve execution speed.

Application about this lesson:complete code

In this example, we’ll create a simple calculator application that allows s to perform basic arithmetic operations using -defined functions.

<!DOCTYPE html>
<html>
<head>
    <title>Calculator Application</title>
</head>
<body>
    <h1>Calculator Application</h1>
    <form id="calculatorForm">
        <label for="num1">Number 1:</label>
        <input type="number" id="num1" name="num1" required><br><br>
        <label for="operator">Operator:</label>
        <select id="operator" name="operator" required>
            <option value="+">+</option>
            <option value="-">-</option>
            <option value="*">*</option>
            <option value="/">/</option>
        </select><br><br>
        <label for="num2">Number 2:</label>
        <input type="number" id="num2" name="num2" required><br><br>
        <button type="button" onclick="calculate()">Calculate</button>
    </form>

    <p id="result"></p>
    <script>
        // -defined function to perform arithmetic operations
        function performOperation(num1, operator, num2) {
            switch (operator) {
                case "+":
                    return num1 + num2;
                case "-":
                    return num1 - num2;
                case "*":
                    return num1 * num2;
                case "/":
                    if (num2 !== 0) {
                        return num1 / num2;
                    } else {
                        return "Cannot divide by zero";
                    }
                default:
                    return "Invalid operator";
            }
        }
        // Function to handle the calculation
        function calculate() {
            const num1 = parseFloat(document.getElementById("num1").value);
            const operator = document.getElementById("operator").value;
            const num2 = parseFloat(document.getElementById("num2").value);
            const result = performOperation(num1, operator, num2);
            document.getElementById("result").textContent = "Result: " + result;
        }
    </script>
</body>
</html>

In this example:

1. The HTML form allows s to input two numbers and select an arithmetic operator.
2. The performOperation function takes the two numbers and the selected operator, performs the corresponding arithmetic operation, and returns the result.
3. The calculate function reads the input values, calls the performOperation function, and displays the result on the web page.

When you open this HTML file in a web browser, you’ll see a calculator application where you can input numbers, select an operator, and calculate the result of the chosen arithmetic operation. This example demonstrates how -defined functions can be used to create interactive applications that perform specific tasks based on  input

multichoice quiz with answers

You can extend and customize this example to create a full-fledged interactive quiz.

<!DOCTYPE html>
<html>
<head>
    <title>-Defined Functions Quiz</title>
</head>
<body>
    <h1>-Defined Functions Quiz</h1>

    <form id="quizForm" onsubmit="return checkAnswers()">
        <h2>Question 1:</h2>
        <p>What is the purpose of -defined functions?</p>
        <input type="radio" name="q1" value="a">A. They are used to define built-in JavaScript functions.<br>
        <input type="radio" name="q1" value="b">B. They allow s to define their own functions for specific tasks.<br>
        <input type="radio" name="q1" value="c">C. They are only used for debugging purposes.<br>

        <h2>Question 2:</h2>
        <p>Which of the following is an advantage of -defined functions?</p>
        <input type="radio" name="q2" value="a">A. They make the code less organized and harder to understand.<br>
        <input type="radio" name="q2" value="b">B. They cannot be reused in other parts of the code.<br>
        <input type="radio" name="q2" value="c">C. They promote modularity, reusability, and maintainability.<br>

        <h2>Question 3:</h2>
        <p>What is the purpose of parameterization in -defined functions?</p>
        <input type="radio" name="q3" value="a">A. To make functions inaccessible to other parts of the code.<br>
        <input type="radio" name="q3" value="b">B. To make functions less flexible and customizable.<br>
        <input type="radio" name="q3" value="c">C. To create functions that can adapt to different scenarios by accepting input values.<br>

        <button type="submit">Submit Answers</button>
    </form>

    <p id="result"></p>

    <script>
        function checkAnswers() {
            const answers = ["b", "c", "c"];
            const form = document.getElementById("quizForm");
            let score = 0;

            for (let i = 0; i < form.elements.length; i++) {
                if (form.elements[i].type === "radio" && form.elements[i].checked) {
                    if (form.elements[i].value === answers[i]) {
                        score++;
                    }
                }
            }

            const result = "You scored " + score + " out of " + answers.length;
            document.getElementById("result").textContent = result;

            // Prevent the form from submitting and refreshing the page
            return false;
        }
    </script>
</body>
</html>

In this example:

1. We have a multi-choice quiz with three questions related to -defined functions.
2. The correct answers are stored in the answers array.
3. The checkAnswers function is called when the submits the quiz. It checks the selected answers against the correct answers and calculates the score.
4. The result of the quiz is displayed on the web page using the document.getElementById(“result”).textContent method.
5. The return false; statement prevents the form from actually submitting and refreshing the page.
6. When you open this HTML file in a web browser, you’ll see the quiz questions, and after selecting answers and submitting, you’ll see your score displayed on the page. You can customize and expand this example to include more questions and options.