JavaScript Functions

Understanding and using functions in JavaScript

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JavaScript Functions

Functions are one of the fundamental building blocks in JavaScript. A function is a reusable block of code that performs a specific task or calculates a value.

Function Declaration

Here's how you can declare a function in JavaScript:

function greet(name) {
console.log("Hello, " + name + "!");
}

greet("Alice"); // Outputs: Hello, Alice!

Function Expression

Functions can also be created using a function expression:

const greet = function(name) {
console.log("Hello, " + name + "!");
};

greet("Bob"); // Outputs: Hello, Bob!

Arrow Functions

Arrow functions provide a more concise syntax for writing function expressions:

const greet = (name) => {
console.log("Hello, " + name + "!");
};

greet("Charlie"); // Outputs: Hello, Charlie!

Function Parameters and Return Values

Functions can take parameters and return values:

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

let result = add(5, 3);
console.log(result); // Outputs: 8

Default Parameters

You can specify default values for function parameters:

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

console.log(sum(1, 2, 3)); // Outputs: 6
console.log(sum(4, 5, 6, 7)); // Outputs: 22

Function Scope

Variables declared inside a function are only accessible within that function:

function exampleFunction() {
let localVar = "I'm local";
console.log(localVar); // Outputs: I'm local
}

console.log(localVar); // Throws an error: localVar is not defined

Closures

Closures allow a function to access variables from an outer function even after the outer function has returned:

function outerFunction(x) {
return function(y) {
return x + y;
}
}

const addFive = outerFunction(5);
console.log(addFive(3)); // Outputs: 8