AI-enhanced Web3 Frontend Development Course

Previous Lesson
Next Lesson

Functions and Scope in JavaScript

 13min
AI-enhanced Web3 Frontend Development Course Functions and Scope in JavaScript

Introduction:

This lesson will guide you through the essentials of creating and using functions, a cornerstone in JavaScript programming, especially relevant in web3 development.

Remember, watching the lesson video will offer a deeper understanding of this topic.

Learning Objectives:

By the end of this lesson, you will be able to:

  1. How to define and call functions in JavaScript.
  2. The concept of function scope, including global and local scopes.
  3. Learn about function hoisting and its nuances in JavaScript.

Lesson Video:

Functions In Javascript:

Functions are the building blocks of JavaScript. They allow you to encapsulate code for specific tasks, leading to more organized, readable, and reusable code.

Declaring Functions:

Functions are declared using the function keyword, followed by a name, parameters, and the function body.

For example:

function square(number) {
  return number * number;
}

Function Expressions:

Functions can also be defined through expressions. These can be named or anonymous and are particularly useful for passing functions as arguments​​.

const square = function(number) {
  return number * number;
};

Function Hoisting:

Function declarations are hoisted to the top of their scope, allowing them to be used before they are defined in the code.

Understanding Scope:

Scope determines the accessibility of variables and functions in JavaScript.

  1. Global Scope: Variables declared outside any function have global scope and can be accessed from anywhere in your code.
  2. Function Scope: Variables declared within a function are limited to that function and cannot be accessed outside of it​​.
  3. Block Scope: Introduced in ES6, let and const provide block scope within curly braces {}. Variables declared with let and const cannot be accessed outside the block they are declared in​​.

Example Codes for Practical Application:

Expanding the Capstone Project

Expanding on our Token Minter dApp, let’s enhance its features using what you learned from this lesson.

Existing Capstone Project Code from Previous Lesson:

Javascript Code:

// External JavaScript file for the global script
 
// Declare a variable to track the total minted tokens
let totalMintedTokens = 0;
 
document.addEventListener('DOMContentLoaded', function() {
    // Access the mint button and input fields
    const mintButton = document.querySelector('#mint button');
    const walletInput = document.querySelector('#walletAddress');
    const tokenInput = document.querySelector('#tokenAmount');
 
    // Event listener for the mint button
    mintButton.addEventListener('click', function() {
        let walletAddress = walletInput.value;
        let tokenAmount = parseInt(tokenInput.value);
 
        // Update the total minted tokens without validation
        updateMintedTokens(tokenAmount);
 
        // Notify the user about the minting process
        alert(`Minting ${tokenAmount} tokens to wallet: ${walletAddress}`);
 
        // TODO: In the next lesson, we will add validation to check the correctness of the wallet address and token amount. 
        // It's important to validate and sometimes sanitize user inputs for security and functionality.
    });
});
 
// Function to update the total minted tokens
function updateMintedTokens(amount) {
    // Add the specified amount to the total minted tokens
    totalMintedTokens += amount;
    document.getElementById('totalMinted').textContent = `Total Minted: ${totalMintedTokens}`;
}

CSS Code:

// External JavaScript file for the global script

// Declare a variable to track the total minted tokens
let totalMintedTokens = 0;

document.addEventListener('DOMContentLoaded', function() {
    // Access the mint button and input fields
    const mintButton = document.querySelector('#mint button');
    const walletInput = document.querySelector('#walletAddress');
    const tokenInput = document.querySelector('#tokenAmount');

    // Event listener for the mint button
    mintButton.addEventListener('click', function() {
        let walletAddress = walletInput.value;
        let tokenAmount = parseInt(tokenInput.value);

        // Validation for wallet address and token amount
        if(walletAddress !== '' && !isNaN(tokenAmount) && tokenAmount > 0) {
            // Update the total minted tokens
            updateMintedTokens(tokenAmount);

            // Notify the user about the minting process
            alert(`Minting ${tokenAmount} tokens to wallet: ${walletAddress}`);
        } else {
            // Alert for invalid input
            alert('Please enter a valid wallet address and a positive number of tokens to mint.');
        }
    });
});

// Function to update the total minted tokens
function updateMintedTokens(amount) {
    // Add the specified amount to the total minted tokens
    totalMintedTokens += amount;
    document.getElementById('totalMinted').textContent = `Total Minted: ${totalMintedTokens}`;
}

HTML Code:

<!DOCTYPE html> <!-- Defines document type and HTML version -->
<html lang="en"> <!-- Sets the language of the page -->

<head>
    <meta charset="UTF-8"> <!-- Sets character encoding for the document -->
    <meta name="viewport" content="width=device-width, initial-scale=1.0"> <!-- Ensures proper rendering on mobile devices -->
    <title>Token Minter dApp</title> <!-- Title of the webpage -->
    <link rel="stylesheet" href="/globalstyles.css"> <!-- Link to external CSS file -->
</head>

<body>
    <header>
        <!-- Site header with navigation -->
        <h1>Token Minter dApp</h1>
        <nav>
            <!-- Navigation links -->
            <ul>
                <li><a href="#home">Home</a></li>
                <li><a href="#mint">Mint Tokens</a></li>
                <li><a href="#about">About</a></li>
            </ul>
        </nav>
    </header>
    
    <main>
        <!-- Main content section -->
        <article id="home">
            <!-- Introduction article -->
            <h2>Introduction to Token Minting</h2>
            <p>This dApp allows users to mint their own tokens on the blockchain.</p>
        </article>
        
        <section id="mint">
            <!-- Token minting form section -->
            <h2>Mint Your Tokens</h2>
            <form action="#">
                <!-- Form for token minting -->
                <input type="email" placeholder="Enter your email">
                <input type="number" placeholder="Token amount">
                <button class="button" type="submit">Mint</button>
            </form>
        </section>
        
        <aside>
            <!-- Sidebar with additional information -->
            <h3>Learn More:</h3>
            <p>Explore more about blockchain technology.</p>
        </aside>
    </main>
    
    <footer>
        <!-- Footer with contact information -->
        <p>Contact us at <a href="mailto:hello@dProgrammingUniversity.com">hello@dProgrammingUniversity.com</a></p>
    </footer>
    
</body>
</html>

Enhance the Capstone Project with New Features from this Lesson:

Javascript Code:

// External JavaScript file for the global script

// Declare variables to track the total minted tokens and set a minting limit
let totalMintedTokens = 0;
const mintingLimit = 10000; // Set a limit for total tokens that can be minted

document.addEventListener('DOMContentLoaded', function() {
    const mintButton = document.querySelector('#mint button');
    const walletInput = document.querySelector('#walletAddress');
    const tokenInput = document.querySelector('#tokenAmount');

    mintButton.addEventListener('click', function() {
        let walletAddress = walletInput.value;
        let tokenAmount = parseInt(tokenInput.value);

        // Validation for wallet address and token amount
        if(walletAddress !== '' && !isNaN(tokenAmount) && tokenAmount > 0) {
            // Call function to update minted tokens and get result
            let mintResult = updateMintedTokens(tokenAmount);

            if(mintResult) {
                // Notify the user about the minting process
                alert(`Minting ${tokenAmount} tokens to wallet: ${walletAddress}`);
            }
        } else {
            // Alert for invalid input
            alert('Please enter a valid wallet address and a positive number of tokens to mint.');
        }
    });
});

// Function to update the total minted tokens
function updateMintedTokens(amount) {
    let successfullyMinted = false;

    // Use a for loop to add tokens to the total, respecting the minting limit
    for(let i = 0; i < amount; i++) {
        if (totalMintedTokens < mintingLimit) {
            totalMintedTokens++;
            successfullyMinted = true;
        } else {
            alert('Minting limit reached. No more tokens can be minted.');
            break; // Exit the loop if the minting limit is reached
        }
    }

    document.getElementById('totalMinted').textContent = `Total Minted: ${totalMintedTokens}`;
    return successfullyMinted;
}

AFTER:

Your code may look something like the following after applying the above adjustment from this lesson:

Javascript Code:

// External JavaScript file for the global script

// Declare variables to track the total minted tokens and set a minting limit
let totalMintedTokens = 0;
const mintingLimit = 10000; // Set a limit for total tokens that can be minted

document.addEventListener('DOMContentLoaded', function() {
    const mintButton = document.querySelector('#mint button');
    const walletInput = document.querySelector('#walletAddress');
    const tokenInput = document.querySelector('#tokenAmount');

    mintButton.addEventListener('click', function() {
        let walletAddress = walletInput.value;
        let tokenAmount = parseInt(tokenInput.value);

        // Validation for wallet address and token amount
        if(walletAddress !== '' && !isNaN(tokenAmount) && tokenAmount > 0) {
            // Call function to update minted tokens and get result
            let mintResult = updateMintedTokens(tokenAmount);

            if(mintResult) {
                // Notify the user about the minting process
                alert(`Minting ${tokenAmount} tokens to wallet: ${walletAddress}`);
            }
        } else {
            // Alert for invalid input
            alert('Please enter a valid wallet address and a positive number of tokens to mint.');
        }
    });
});

// Function to update the total minted tokens
function updateMintedTokens(amount) {
    let successfullyMinted = false;

    // Use a for loop to add tokens to the total, respecting the minting limit
    for(let i = 0; i < amount; i++) {
        if (totalMintedTokens < mintingLimit) {
            totalMintedTokens++;
            successfullyMinted = true;
        } else {
            alert('Minting limit reached. No more tokens can be minted.');
            break; // Exit the loop if the minting limit is reached
        }
    }

    document.getElementById('totalMinted').textContent = `Total Minted: ${totalMintedTokens}`;
    return successfullyMinted;
}

CSS Code:

/* External CSS */
 
/* IMPORTS */
@import url('https://fonts.googleapis.com/css2?family=Roboto:wght@400;700&display=swap');
 
/* CSS Variables for consistent theming and easy maintenance */
:root {
    --font-family: 'Roboto', sans-serif;
    --bg-color: #f4f4f4;
    --bg-gradient: linear-gradient(to right, #630404, #e040fb, #6a027c);
    --nav-hover-bg-color: #630404;
    --nav-hover-text-color: #f3e40d;
    --text-color-white: #ffffff;
    --header-bg-color: #333;
    --header-text-color: white;
    --subtitle-text-color: #aaa;
    --paragraph-color: #cfbdbd;
    --main-border-color: #333;
    --article-border-color: grey;
    --form-border-color: #ddd;
    --input-border-color: #ccc;
    --button-hover-color: #f5f121;
    --invalid-input-border-color: red;
    --placeholder-color: #888;
    --info-text-color: #521f1f;
}
 
/* BODY */
body {
    font-family: var(--font-family);
    background-color: var(--bg-color);
    background: var(--bg-gradient);
}
 
/* NAVIGATION */
nav > ul > li {
    display: inline;
    margin-right: 20px;
    text-align: center;
    padding: 10px;
    flex: 1;
}
 
nav a:hover, nav a:focus {
    background-color: var(--nav-hover-bg-color);
    color: var(--nav-hover-text-color);
}
 
/* HYPERLINKS */
a[href^="#"] {
    text-decoration: none;
    color: var(--text-color-white);
}
 
/* HEADINGS */
header {
    background: var(--header-bg-color);
    color: var(--header-text-color);
    padding: 10px;
    text-align: center;
    display: flex;
    justify-content: space-between;
    align-items: center;
}
 
h1 {
    font-weight: 700;
    position: relative;
}
 
h1::after {
    content: '...the future of token minting';
    display: block;
    text-align: center;
    color: var(--subtitle-text-color);
    position: absolute;
    width: 100%;
    left: 0;
    top: 100%;
    font-size: 0.55em;
}
 
h1, h2, h3 {
    font-weight: 700;
}
 
h2 + p {
    color: var(--paragraph-color);
}
 
/* MAIN */
main {
    display: flex;
    flex-direction: row;
    gap: 10px;
}
 
/* ARTICLE */
article {
    margin-bottom: 15px;
    padding: 10px;
    border: 1px solid var(--article-border-color);
    flex: 1;
}
 
article p {
    margin-bottom: 20px;
    border: 1px solid var(--article-border-color);
    padding: 15px;
}
 
/* IDs */
#mint {
    background-color: #eaeaea;
    padding: 15px;
    margin-top: 10px;
}
 
#mint form {
    padding: 10px;
    border: 1px solid var(--form-border-color);
    margin-top: 10px;
    display: flex;
    flex-direction: column;
    gap: 10px;
}
 
#mint input,
#mint button {
    padding: 10px;
    margin-bottom: 10px;
    border: 1px solid var(--input-border-color);
    flex: 1;
}

#totalMinted {
    color: var(--info-text-color);
}
 
/* PARAGRAPH */
p {
    line-height: 3.5;
}
 
/* MEDIA QUERY */
@media (min-width: 768px) and (max-width: 1024px) {
    body {
        background: var(--bg-gradient);
    }
    main {
        flex-direction: row;
    }
}
 
@media (max-width: 767px) {
    nav ul {
        flex-direction: column;
    }
    .button {
        padding: 15px;
    }
}
 
/* ANIMATION AND TRANSITION */
@keyframes pulse {
    0% { transform: scale(1); }
    50% { transform: scale(1.1); }
    100% { transform: scale(1); }
}
 
.button {
    animation: pulse 2s infinite;
}
 
a {
    transition: color 0.5s ease;
}
 
a:hover {
    color: var(--button-hover-color);
}
 
@media (max-width: 600px) {
    .container {
        flex-direction: column;
    }
}
 
input:invalid {
    border-color: var(--invalid-input-border-color);
}
 
::placeholder {
    color: var(--placeholder-color);
    opacity: 1;
}

HTML Code:

<!DOCTYPE html> <!-- Defines document type and HTML version -->
<html lang="en"> <!-- Sets the language of the page -->
 
<head>
    <meta charset="UTF-8"> <!-- Sets character encoding for the document -->
    <meta name="viewport" content="width=device-width, initial-scale=1.0"> <!-- Ensures proper rendering on mobile devices -->
    <title>Token Minter dApp</title> <!-- Title of the webpage -->
    <link rel="stylesheet" href="/globalstyles.css"> <!-- Link to external CSS file -->
    <script src="/globalscript.js"></script> <!-- Link to external CSS file -->
</head>
 
<body>
    <header>
        <!-- Site header with navigation -->
        <h1>Token Minter dApp</h1>
        <nav>
            <!-- Navigation links -->
            <ul>
                <li><a href="#home">Home</a></li>
                <li><a href="#mint">Mint Tokens</a></li>
                <li><a href="#about">About</a></li>
            </ul>
        </nav>
    </header>
     
    <main>
        <!-- Main content section -->
        <article id="home">
            <!-- Introduction article -->
            <h2>Introduction to Token Minting</h2>
            <p>This dApp allows users to mint their own tokens on the blockchain.</p>
        </article>
         
        <section id="mint">
            <!-- Token minting form section -->
            <h2>Mint Your Tokens</h2>
            <form action="#">
                <!-- Form for token minting -->
                <input type="text" placeholder="Enter your wallet address" id="walletAddress">
                <input type="number" placeholder="Token amount" id="tokenAmount">
                <button class="button" type="button">Mint</button>
            </form>
            <p id="totalMinted">Total Minted: 0</p>
        </section>
         
        <aside>
            <!-- Sidebar with additional information -->
            <h3>Learn More:</h3>
            <p>Explore more about blockchain technology.</p>
        </aside>
    </main>
     
    <footer>
        <!-- Footer with contact information -->
        <p>Contact us at <a href="mailto:hello@dProgrammingUniversity.com">hello@dProgrammingUniversity.com</a></p>
    </footer>
</body>
</html>

Conclusion:

Understanding JavaScript functions and scope is pivotal in building robust and efficient web3 applications.

This knowledge will empower you to write organized, scalable, and secure code for your dApps/dWebs.

Resources & References:

To deepen your understanding of this lesson, you can explore the following resources:

  1. JavaScript Functions and Scope – a Beginner’s Guide
  2. Functions – JavaScript | MDN
  3. MDN Web Docs – JavaScript Basics reference
  4. W3Schools – JavaScript Tutorial
  5. Freecodecamp – JavaScript Handbook

These resources provide comprehensive guides and examples that will be invaluable as you learn and apply them in your journey of Web3 frontend development.

Support:

If you need help with this lesson, questions, suggestions and improvement. The best way to get help is to use the comment below:
1. First check existing comments if your questions have been answered before posting.
2. If no existing related question with an answer, then you can post a new one (kindly avoid duplicating previously asked and answered questions).

NOTE: This is the most recommended way of getting support directly from the instructor of this course. Posting on other platforms like Discord may get support from other community members and not from the course instructor directly.

Images|Videos|Links: To support your question with a screenshot, Github repo link or other media, kindly upload it somewhere online like Drive/Dropbox or Github (for codes) first, then post the link to it in your comment. Please do not upload media/codes directly, it may fail or cause your comment to be deleted.

Please ONLY post questions that are specific to this lesson not the entire course to ensure others can find it helpful. Each lesson allows comments relating to it ONLY. Off-lesson questions will be deleted even if they relate to this course as a whole but as long as they are not specific to this lesson, they are not allowed.

Lesson Content
Previous Lesson
Back to Course
Next Lesson
2 Comments
Collapse Comments
User Avatar Gideon Okorie June 21, 2024 at 9:52 am

Please it is typescript questions that asked in this quiz, it should be an error

Solomon Foskaay (Administrator) June 26, 2024 at 5:31 pm

Noted.

Leave a Comment

By using this website you agree to accept our Privacy Policy and Terms & Conditions