🧠 JavaScript Smart Function Parameters – Default, Rest & Destructuring Explained

💡 Smart parameters help you handle optional, default, and flexible inputs in a cleaner way, reducing the need for manual checks inside the function.

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✅ 1. Default Parameters in JavaScript

📌 Code Example:

function greet(name = "Guest") {
  console.log(`Hello, ${name}!`);
}

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

🧩 Explanation:

• name = "Guest" assigns a default value if no argument is passed.
• greet(); → logs “Hello, Guest”
• greet("Alice"); → overrides the default with “Alice”

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✅ 2. Object Destructuring in Function Parameters

📌 Code Example:

function createUser({ name, age, country = "Unknown" }) {
  console.log(`Name: ${name}, Age: ${age}, Country: ${country}`);
}

createUser({ name: "Bob", age: 30 }); // Country defaults to "Unknown"

🧩 Explanation:

• Destructures an object argument into name, age, and country
• country has a default value if not passed

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✅ 3. Array Destructuring in Function Parameters

📌 Code Example:

function showScores([first, second, third = 0]) {
  console.log(`Gold: ${first}, Silver: ${second}, Bronze: ${third}`);
}

showScores([100, 80]); // third defaults to 0

🧩 Explanation:

• Unpacks an array directly into variables
• third defaults to 0 if not provided

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✅ 4. JavaScript Rest Parameters

📌 Code Example:

function sumAll(...numbers) {
  return numbers.reduce((total, num) => total + num, 0);
}

console.log(sumAll(1, 2, 3, 4)); // Output: 10

🧩 Explanation:

• ...numbers gathers all arguments into an array
• .reduce() calculates the sum

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✅ 5. Short-Circuit Parameter Validation

📌 Code Example:

function printMessage(msg) {
  msg = msg || "Default Message";
  console.log(msg);
}

printMessage();             // Output: Default Message
printMessage("Hello!");     // Output: Hello!

🧩 Explanation:

• Uses logical OR to assign a default if msg is falsy
• Common technique before default parameter syntax became standard

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✅ 6. Combining Destructuring with Defaults

📌 Code Example:

function configure({ theme = "light", layout = "grid" } = {}) {
  console.log(`Theme: ${theme}, Layout: ${layout}`);
}

configure(); // Output: Theme: light, Layout: grid

🧩 Explanation:

• Sets defaults for both the entire object and its properties
• Prevents runtime errors if function is called with undefined

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📘 Best Practices for Smart Parameters

✅ Prefer default parameters over conditional assignments
✅ Use object destructuring for readability in configuration objects
✅ Apply array destructuring for ordered data like scores or coordinates
✅ Use rest parameters for flexible, variadic functions
✅ Combine patterns wisely for clarity and fallback safety

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🧠 Summary

Smart Function Parameters in JavaScript (ES6+) offer:

• 🧼 Cleaner code without redundant checks
• 🔧 Flexible function signatures
• 🛡️ Resilience against missing or undefined arguments

These patterns are essential in building scalable and readable modern JavaScript functions.

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❓ FAQs – Smart Function Parameters in JavaScript

❓ What are default parameters in JavaScript?

Default parameters allow you to set a default value if no argument is provided for that parameter during the function call.

❓ Can you use destructuring in function parameters?

Yes! You can destructure both objects and arrays directly in the parameter list to extract values conveniently.

❓ What is the use of rest parameters?

Rest parameters collect all remaining arguments into an array, useful for functions that accept an arbitrary number of inputs.

❓ Is short-circuiting with || still useful?

Yes. While ES6 default parameters are preferred, || short-circuiting is still widely used for backward compatibility or conditional fallbacks.

❓ How can I combine destructuring and defaults?

Wrap the destructured object in a default:

function config({ theme = 'light' } = {}) {}

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