Base64 in JavaScript - Practical Examples

// BASIC ENCODING & DECODING

JavaScript provides built-in functions for Base64 operations. The btoa() and atob() functions handle basic encoding and decoding:

These functions work great for ASCII text, but require special handling for Unicode characters.

// Basic Base64 encoding
const text = 'Hello World';
const encoded = btoa(text);
console.log(encoded); // SGVsbG8gV29ybGQ=

// Basic Base64 decoding
const decoded = atob(encoded);
console.log(decoded); // Hello World

// Check if string is valid Base64
function isValidBase64(str) {
    try {
        return btoa(atob(str)) === str;
    } catch (err) {
        return false;
    }
}

// UNICODE SUPPORT

For Unicode strings, we need to convert to UTF-8 bytes first. Modern browsers provide TextEncoder and TextDecoder APIs:

This approach correctly handles emoji, international characters, and other Unicode content.

// Unicode-safe Base64 encoding
function encodeBase64(str) {
    const encoder = new TextEncoder();
    const bytes = encoder.encode(str);
    const binary = String.fromCharCode(...bytes);
    return btoa(binary);
}

// Unicode-safe Base64 decoding
function decodeBase64(base64) {
    const binary = atob(base64);
    const bytes = new Uint8Array(binary.length);
    for (let i = 0; i < binary.length; i++) {
        bytes[i] = binary.charCodeAt(i);
    }
    const decoder = new TextDecoder();
    return decoder.decode(bytes);
}

// Example with emoji
const emoji = 'Hello 👋 World 🌍';
const encoded = encodeBase64(emoji);
const decoded = decodeBase64(encoded);
console.log(decoded); // Hello 👋 World 🌍

// FILE HANDLING

Converting files to Base64 is common for uploads and data URIs. Use FileReader API for client-side file processing:

This creates data URIs that can be embedded directly in HTML or sent to APIs.

// Convert file to Base64 data URI
function fileToBase64(file) {
    return new Promise((resolve, reject) => {
        const reader = new FileReader();
        reader.onload = () => resolve(reader.result);
        reader.onerror = error => reject(error);
        reader.readAsDataURL(file);
    });
}

// Usage with file input
document.getElementById('fileInput').addEventListener('change', async (e) => {
    const file = e.target.files[0];
    if (file) {
        try {
            const base64 = await fileToBase64(file);
            console.log(base64);
            // Result: data:image/png;base64,iVBORw0KGgoAAAA...
        } catch (error) {
            console.error('Error:', error);
        }
    }
});

// URL-SAFE BASE64

Standard Base64 uses + and / characters that need URL encoding. URL-safe Base64 replaces these with - and _:

This is essential for tokens, IDs, and other data transmitted via URLs.

// Convert to URL-safe Base64
function toUrlSafeBase64(base64) {
    return base64
        .replace(/\+/g, '-')
        .replace(/\//g, '_')
        .replace(/=/g, '');
}

// Convert from URL-safe Base64
function fromUrlSafeBase64(urlSafeBase64) {
    let base64 = urlSafeBase64
        .replace(/-/g, '+')
        .replace(/_/g, '/');
    
    // Add padding if needed
    const padding = 4 - (base64.length % 4);
    if (padding !== 4) {
        base64 += '='.repeat(padding);
    }
    
    return base64;
}

// Example
const text = 'URL-safe encoding test';
const encoded = btoa(text);
const urlSafe = toUrlSafeBase64(encoded);
console.log(urlSafe); // VVJMLXNhZmUgZW5jb2RpbmcgdGVzdA

// STREAMING LARGE DATA

For large files or data streams, process in chunks to avoid memory issues:

This approach prevents browser freezing and handles large datasets efficiently.

// Stream-based Base64 encoding
class Base64Encoder {
    constructor() {
        this.buffer = '';
    }
    
    encode(chunk) {
        this.buffer += chunk;
        const completeBytes = Math.floor(this.buffer.length / 3) * 3;
        const toEncode = this.buffer.slice(0, completeBytes);
        this.buffer = this.buffer.slice(completeBytes);
        
        return btoa(toEncode);
    }
    
    flush() {
        if (this.buffer.length > 0) {
            const result = btoa(this.buffer);
            this.buffer = '';
            return result;
        }
        return '';
    }
}

// Usage
const encoder = new Base64Encoder();
let result = '';
result += encoder.encode('First chunk');
result += encoder.encode(' Second chunk');
result += encoder.flush();
console.log(result);

// ERROR HANDLING

Always implement proper error handling for Base64 operations:

Robust error handling prevents application crashes and provides better user experience.

// Safe Base64 operations with error handling
function safeEncode(input) {
    try {
        if (typeof input !== 'string') {
            throw new Error('Input must be a string');
        }
        return btoa(input);
    } catch (error) {
        console.error('Encoding error:', error.message);
        return null;
    }
}

function safeDecode(base64) {
    try {
        // Validate Base64 format
        if (!/^[A-Za-z0-9+/]*={0,2}$/.test(base64)) {
            throw new Error('Invalid Base64 format');
        }
        return atob(base64);
    } catch (error) {
        console.error('Decoding error:', error.message);
        return null;
    }
}

// Usage
const encoded = safeEncode('Hello World');
const decoded = safeDecode(encoded);
if (encoded && decoded) {
    console.log('Success:', decoded);
}