<p>Prefers video content? Here are the 5 SOLID programming principles explained, applied to JavaScript (in English)</p>

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<p>Modern JavaScript in 2025 demands more than just “making code work.”</p>

<p>We now build scalable front-end apps, distributed back-ends, microservices, serverless functions, and highly interactive UIs. As systems grow, readability and maintainability become far more valuable than simply shipping features.<br>
That’s where SOLID principles + clean code practices make the biggest difference.</p>

<p>In this guide, you’ll learn:</p>

<p>What SOLID means (in simple language)<br>
Real-world JavaScript examples<br>
Modern 2025 patterns (ES modules, async workflows, classes, composition)</p>

<p>How to write cleaner, maintainable, testable code</p>

<p>How developers in 2025 use tools like AI, linting, and even picture text tools to streamline their workflow</p>

<p>Let’s begin.</p>
<h3>
  
  
  Table of Contents
</h3>

<ol>
<li>What is Clean Code (2025 Definition)?</li>
<li>Why SOLID Still Matters in Modern JavaScript</li>
<li>- S — Single Responsibility Principle (with ES6 example)</li>
<li>- O — Open/Closed Principle (with real pattern)</li>
<li>- L — Liskov Substitution Principle (practical example)</li>
<li>- I — Interface Segregation Principle (JS-friendly explanation)</li>
<li>- D — Dependency Inversion Principle (modern Node.js example)</li>
<li>- Clean Code Best Practices for 2025</li>
<li>- Bonus: Modern Tools That Make Clean Code Easier</li>
<li>- Final Summary</li>
</ol>
<h2>
  
  
  1. What Is Clean Code in 2025?
</h2>

<p>The concept has evolved.<br>
 Clean code in 2025 is:<br>
✔ Easy to read<br>
 ✔ Easy to test<br>
 ✔ Easy to extend<br>
 ✔ Easy to refactor<br>
 ✔ Easy for AI tools to understand and refactor<br>
 ✔ Predictable and consistent<br>
 ✔ Uses modern syntax (modules, async/await, classes, immutability)<br>
Think of it like writing instructions for your future self. Or for your team. When you come back to it in six months, you should still understand exactly what you were doing.</p>
<h2>
  
  
  2. Why SOLID Still Matters in JavaScript (Even in 2025)
</h2>

<p>Despite JavaScript being flexible, dynamic, and sometimes chaotic:<br>
Front-end apps are bigger (React/Next.js, Vue, Svelte)</p>

<p>Back-end services are more distributed (Node.js, Deno)</p>

<p>AI-driven applications involve modular pipelines</p>

<p>SOLID principles prevent messy “spaghetti JavaScript” and turn your code into:<br>
✔ predictable<br>
 ✔ modular<br>
 ✔ maintainable<br>
 ✔ scalable<br>
SOLID isn’t outdated — it’s more important than ever.</p>
<h2>
  
  
  3. S — Single Responsibility Principle (SRP)
</h2>

<p>A module/class/function should have only ONE reason to change.</p>
<h3>
  
  
  ❌ Bad Example
</h3>


<div class="highlight js-code-highlight">
<pre class="highlight plaintext"><code>function processOrder(order) {
  const total = order.items.reduce((sum, i) =&gt; sum + i.price, 0);
  saveToDatabase(order);
  sendEmail(order.userEmail);
  return total;
}
</code></pre>

</div>


<p>This function does:</p>

<ul>
<li>calculation</li>
<li>persistence</li>
<li>email sending</li>
<li>Three responsibilities mixed = hard to test &amp; maintain.</li>
</ul>
<h3>
  
  
  ✔ Good 2025 Example (Cleaner)
</h3>


<div class="highlight js-code-highlight">
<pre class="highlight plaintext"><code>function calculateTotal(order) {
  return order.items.reduce((sum, i) =&gt; sum + i.price, 0);
}

function saveOrder(orderRepository, order) {
  return orderRepository.save(order);
}

function notifyUser(notificationService, email) {
  return notificationService.send(email);
}
</code></pre>

</div>


<p>Each function is focused.<br>
 Testing becomes easy.</p>
<h2>
  
  
  4. O — Open/Closed Principle (OCP)
</h2>

<p>Code should be open for extension but closed for modification.<br>
Meaning:<br>
 ➡ You shouldn’t rewrite old logic<br>
 ➡ You should extend it with new behavior</p>
<h3>
  
  
  ❌ Bad
</h3>


<div class="highlight js-code-highlight">
<pre class="highlight plaintext"><code>function pay(price, method) {
  if (method === "card") return cardPayment(price);
  if (method === "paypal") return payPalPayment(price);
}

</code></pre>

</div>


<p>Every time you add a new method, you modify this function.</p>
<h3>
  
  
  ✔ Good 2025 Example — Strategy Pattern
</h3>


<div class="highlight js-code-highlight">
<pre class="highlight plaintext"><code>class PaymentProcessor {
  constructor(strategy) {
    this.strategy = strategy;
  }

  pay(amount) {
    return this.strategy.pay(amount);
  }
}

class PayPalPayment {
  pay(amount) { /* ... */ }
}

class CryptoPayment {
  pay(amount) { /* ... */ }
}
</code></pre>

</div>


<p>Add as many payment classes as you want — no modification needed.</p>
<h2>
  
  
  5. L — Liskov Substitution Principle (LSP)
</h2>

<p>If class B extends class A, it must behave like A.</p>
<h3>
  
  
  ❌ Bad Example
</h3>


<div class="highlight js-code-highlight">
<pre class="highlight plaintext"><code>class Rectangle {
  setWidth(w) { this.width = w; }
  setHeight(h) { this.height = h; }
}

class Square extends Rectangle {
  setWidth(w) { this.width = this.height = w; }
}

</code></pre>

</div>


<p>Violates expectations.</p>

<p>A Rectangle consumer expects width &amp; height independently.</p>
<h3>
  
  
  ✔ Good Example
</h3>

<p>Use a separate abstraction:<br>
</p>

<div class="highlight js-code-highlight">
<pre class="highlight plaintext"><code>class Shape {
  area() {}
}

class Rectangle extends Shape {
  constructor(w, h) { super(); this.w = w; this.h = h; }
  area() { return this.w * this.h; }
}

class Square extends Shape {
  constructor(s) { super(); this.s = s; }
  area() { return this.s * this.s; }
}
</code></pre>

</div>



<p>Both can substitute Shape.</p>

<h2>
  
  
  6. I — Interface Segregation Principle (ISP)
</h2>

<p>Don’t force classes to implement methods they don’t use.<br>
In JavaScript, we simulate this using small, focused modules instead of “god classes.”</p>

<h3>
  
  
  ❌ Bad
</h3>



<div class="highlight js-code-highlight">
<pre class="highlight plaintext"><code>class Product {
  saveToDb() {}
  displayInUI() {}
}
</code></pre>

</div>



<p>Digital products might not need DB saving.</p>

<h3>
  
  
  ✔ Good (2025 Modular Approach)
</h3>



<div class="highlight js-code-highlight">
<pre class="highlight plaintext"><code>class UIProduct {
  render() { /* ... */ }
}

class DBProduct {
  save() { /* ... */ }
}
</code></pre>

</div>



<p>Small pieces are better.</p>

<h2>
  
  
  7. D — Dependency Inversion Principle (DIP)
</h2>

<p>High-level modules should be built around abstractions rather than tied to specific implementations.</p>

<h3>
  
  
  ❌ Bad
</h3>



<div class="highlight js-code-highlight">
<pre class="highlight plaintext"><code>class FileLogger {
  write() {}
}

class UserService {
  constructor() {
    this.logger = new FileLogger(); 
  }
}

</code></pre>

</div>



<p>Hard to test — tied to file logging.</p>

<h3>
  
  
  ✔ Good 2025 Example — Pass Dependencies
</h3>



<div class="highlight js-code-highlight">
<pre class="highlight plaintext"><code>class UserService {
  constructor(logger) {
    this.logger = logger;
  }
}

class ConsoleLogger {
  write(msg) { console.log(msg); }
}

const userService = new UserService(new ConsoleLogger());

</code></pre>

</div>



<p>Easy to mock.<br>
 Easy to replace.<br>
 Clean architecture.</p>

<h2>
  
  
  8. Clean Code Best Practices for 2025
</h2>

<p>👉 Use ES modules (import/export)<br>
👉 Use async/await consistently<br>
 👉 Prefer pure functions<br>
 👉 Use composition over inheritance<br>
 👉 Use descriptive names<br>
 👉 Avoid deeply nested callbacks<br>
 👉 Keep functions under 20–30 lines<br>
 👉 Use TypeScript if possible<br>
 👉 Keep files small and focused<br>
 👉 Write tests for business logic</p>

<h2>
  
  
  9. Bonus: Modern Tools That Make Clean Code Easier
</h2>

<p>Here are must-use tools in 2025:</p>

<ul>
<li>ESLint + Prettier (format + lint)</li>
<li>Jest / Vitest (testing)</li>
<li>Playwright (E2E)</li>
<li>AI-assisted refactoring</li>
<li>Tools that pull text from screenshots or images, like <a href="https://picturetext.org/" rel="noopener noreferrer">PictureText</a>,can help. They’re great when you need to convert a code screenshot into actual editable text.
These accelerate your development workflow.</li>
</ul>

<h2>
  
  
  10. Conclusion
</h2>

<p>SOLID isn’t outdated — it’s the foundation of clean, scalable JavaScript in 2025.</p>

<p>By applying these principles with modern JS syntax:</p>

<p>✔ Your code becomes predictable<br>
 ✔ Your apps become scalable<br>
 ✔ Your team becomes faster<br>
 ✔ Your future self becomes grateful</p>

<p>Clean code is not perfection — it’s consistency and clarity.</p>

يتناول المقال أهمية مبادئ SOLID وممارسات كتابة الكود النظيف في تطوير جافا سكريبت الحديثة اعتبارًا من عام 2025. ويؤكد أن إنشاء تطبيقات واجهة أمامية قابلة للتوسع، وواجهات خلفية موزعة، وميكروسيرفيس، ووظائف بدون خادم، وواجهات مستخدم تفاعلية يتطلب أكثر من مجرد كود يعمل؛ فقراءة الكود وصيانته أمران حاسمان. يقدم الدليل رؤى حول معنى SOLID، ويقدم أمثلة واقعية لجافا سكريبت، ويقدم أنماطًا حديثة مثل وحدات ES وتدفقات العمل غير المتزامنة. بالإضافة إلى ذلك، يبرز كيف يمكن للمطورين استخدام أدوات مثل الذكاء الاصطناعي وأدوات التنسيق لتحسين سير عملهم في البرمجة.

El artículo aborda la importancia de los principios SOLID y las prácticas de código limpio en el desarrollo moderno de JavaScript en 2025. Enfatiza que crear aplicaciones front-end escalables, back-ends distribuidos, microservicios, funciones sin servidor e interfaces de usuario interactivas requiere más que solo código funcional; la legibilidad y mantenibilidad son cruciales. La guía ofrece información sobre lo que significa SOLID, proporciona ejemplos de JavaScript del mundo real e introduce patrones modernos como módulos ES y flujos de trabajo asíncronos. Además, destaca cómo los desarrolladores pueden utilizar herramientas como IA y linting para mejorar su flujo de trabajo de codificación.

L'article aborde l'importance des principes SOLID et des pratiques de code propre dans le développement JavaScript moderne en 2025. Il souligne que la création d'applications front-end évolutives, de back-ends distribués, de microservices, de fonctions sans serveur et d'interfaces utilisateur interactives nécessite plus qu'un code fonctionnel ; la lisibilité et la maintenabilité sont essentielles. Le guide offre des éclaircissements sur la signification de SOLID, fournit des exemples concrets de JavaScript et introduit des modèles modernes tels que les modules ES et les flux de travail asynchrones. De plus, il met en avant comment les développeurs peuvent utiliser des outils comme l'IA et le linting pour améliorer leur flux de travail de codage.

The article discusses the importance of SOLID principles and clean code practices in modern JavaScript development as of 2025. It emphasizes that creating scalable front-end applications, distributed back-ends, microservices, serverless functions, and interactive UIs requires more than just functional code; readability and maintainability are crucial. The guide offers insights into what SOLID means, provides real-world JavaScript examples, and introduces modern patterns such as ES modules and async workflows. Additionally, it highlights how developers can utilize tools like AI and linting to enhance their coding workflow.

The Only SOLID + Clean Code JavaScript Guide You Need in 2025

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