In JavaScript, functions are reusable blocks of code that perform a specific task or calculate a value. They are fundamental to JavaScript programming and are used to organize code, improve code reusability, and implement modular design patterns. Here's an overview of functions in JavaScript along with examples:
1. Function Declaration:
// Syntax: function functionName(parameters) { code to be executed }
function greet(name) {
console.log("Hello, " + name + "!");
}
// Calling the function
greet("Alice"); // Output: Hello, Alice!
2. Function Expression:
// Anonymous function expression
let greet = function(name) {
console.log("Hello, " + name + "!");
};
// Named function expression
let greet = function greet(name) {
console.log("Hello, " + name + "!");
};
// Calling the function
greet("Bob"); // Output: Hello, Bob!
3. Arrow Functions (Introduced in ES6):
// Syntax: const functionName = (parameters) => { code to be executed }
const greet = (name) => {
console.log("Hello, " + name + "!");
};
// Calling the function
greet("Charlie"); // Output: Hello, Charlie!
4. Returning Values:
function add(a, b) {
return a + b;
}
let result = add(5, 3);
console.log(result); // Output: 8
5. Default Parameters:
function greet(name = "Guest") {
console.log("Hello, " + name + "!");
}
greet(); // Output: Hello, Guest!
greet("David"); // Output: Hello, David!
6. Rest Parameters:
function sum(...numbers) {
let total = 0;
for (let num of numbers) {
total += num;
}
return total;
}
console.log(sum(1, 2, 3)); // Output: 6
console.log(sum(10, 20, 30, 40)); // Output: 100
7. Function Scope and Closures:
function outerFunction() {
let outerVar = "I'm from outer function";
function innerFunction() {
console.log(outerVar);
}
return innerFunction;
}
let innerFunc = outerFunction();
innerFunc(); // Output: I'm from outer function
These examples cover the basic concepts of functions in JavaScript. Functions are versatile and powerful in JavaScript, allowing developers to create complex applications with ease.
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