JavaScript Functions: A Complete Guide

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JS Functions

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A function in JavaScript is a reusable block of code designed to perform a specific task. Functions make code modular, readable, and reusable.

Syntax:

function functionName(parameters) {
  // Function body
  return value;
}

Function Declaration:

A function declaration defines a named function using the function keyword.

Example

function greet(name) {

return `Hello, ${name}!`;

}

console.log(greet("Alice")); // Output: Hello, Alice!

Try it yourself

Function Expression:

A function expression assigns a function to a variable.

Syntax:

const functionName = function(parameters) {
  // Function body
  return value;
}

Example

let greet = function(name) {

return `Hello, ${name}!`;

}

console.log(greet("Alice")); // Output: Hello, Alice!

Try it yourself

Arrow Functions (ES6):

Arrow functions provide a shorter syntax and automatically bind this.

Syntax:

const functionName = (parameters) => {
  // Function body
};

Example

const add = (a, b) => {

return a + b;

};

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

// Single Parameter: Parentheses can be omitted

const greet = name => `Hello, ${name}`;

console.log(greet('Alice')); // Output: Hello, Alice!

// No Parameters: Use empty parentheses

const sayHi = () => console.log("Hi!");

sayHi();

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Immediately Invoked Function Expressions (IIFE):

An IIFE runs immediately after being defined.

Example

(function() {

console.log("I am an IIFE!"); // Output: I am an IIFE!

})();

// Arrow Function IIFE:

(() => {

console.log("IIFE with Arrow Function!"); // Output: IIFE with Arrow Function!

})();

Try it yourself

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