JavaScript

In JavaScript, function parameters are the named variables listed in the function definition. They act as placeholders for the values (called arguments) that will be passed into the function when it’s invoked.

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🧱 Basic Syntax

function greet(name) {
  console.log(`Hello, ${name}`);
}

Here, name is a parameter. When calling greet("Alice"), "Alice" is the argument passed to the function.

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🧠 Multiple Parameters

You can define multiple parameters separated by commas:

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

console.log(add(5, 3)); // 8

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⚙️ Default Parameters (ES6)

You can assign default values to parameters in case no argument is passed:

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

greet();        // Hello, Guest
greet("Sam");   // Hello, Sam

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📦 Rest Parameters (...)

When you want to pass an unknown number of arguments, use the rest parameter syntax (...):

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

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

🔹 It gathers all remaining arguments into an array.

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🔍 Arguments Object (Old Way)

Every non-arrow function gets a built-in arguments object:

function showAll() {
  console.log(arguments);
}

showAll(1, 2, 3); // [1, 2, 3]

⚠️ Note:

• arguments is array-like, not a real array
• Not available in arrow functions

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💡 Destructuring Parameters

You can extract values from objects or arrays directly in the parameter list.

✅ Object Destructuring:

function displayUser({ name, age }) {
  console.log(`${name} is ${age} years old.`);
}

displayUser({ name: "John", age: 30 });

✅ Array Destructuring:

function sum([a, b]) {
  return a + b;
}

console.log(sum([3, 7])); // 10

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✅ Summary

Feature	Description
Regular Parameters	Named variables in function definition
Default Parameters	Provide fallback values if no argument is passed
Rest Parameters	Capture multiple arguments into a single array
arguments Object	Legacy method to access passed values (not in arrow funcs)
Destructuring	Extract values from arrays/objects right in parameters

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🔁 Example Combining All Concepts

function introduce({ name = "Guest", age = 0 }, ...skills) {
  console.log(`${name} is ${age} years old.`);
  console.log("Skills:", skills.join(", "));
}

introduce({ name: "Alice", age: 25 }, "JavaScript", "React", "CSS");

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