J

Funciones

JavaScript syntax guide

Declaraciones y expresiones de funciones en JavaScript

Funciones

Declaraciones y expresiones de funciones en JavaScript

JavaScript funciones (javascript)
        
          // 1. FUNCTION DECLARATIONS (Hoisted)
function greet(name) {
  return `Hello, ${name}!`;
}

// Function declarations are hoisted (can be called before definition)
console.log(greet("Alice")); // ✅ Works: "Hello, Alice!"

// 2. FUNCTION EXPRESSIONS (Not hoisted)
const greetExpression = function(name) {
  return `Hello, ${name}!`;
};

// Anonymous function expression
const square = function(x) {
  return x * x;
};

// Named function expression (useful for debugging)
const factorial = function fact(n) {
  return n <= 1 ? 1 : n * fact(n - 1);
};

// 3. ARROW FUNCTIONS (ES6+)
const greetArrow = (name) => `Hello, ${name}!`;
const add = (a, b) => a + b;
const getUser = () => ({ name: "John", age: 30 }); // Return object

// Arrow functions don't have their own 'this'
const person = {
  name: "Alice",
  greet: function() {
    setTimeout(() => {
      console.log(`Hello, I'm ${this.name}`); // ✅ 'this' refers to person
    }, 1000);
  }
};

// 4. DEFAULT PARAMETERS
function createUser(name, role = "user", active = true) {
  return { name, role, active };
}

createUser("John");           // { name: "John", role: "user", active: true }
createUser("Jane", "admin");  // { name: "Jane", role: "admin", active: true }

// 5. REST PARAMETERS (...args)
function sum(...numbers) {
  return numbers.reduce((total, num) => total + num, 0);
}

sum(1, 2, 3);      // 6
sum(10, 20, 30, 40); // 100

function logArguments(first, second, ...others) {
  console.log(first, second, others);
}

logArguments(1, 2, 3, 4, 5); // 1, 2, [3, 4, 5]

// 6. IMMEDIATELY INVOKED FUNCTION EXPRESSIONS (IIFE)
(function() {
  const privateVar = "I'm private";
  console.log(privateVar);
})();

// IIFE with parameters
const result = (function(a, b) {
  return a + b;
})(5, 10);

// 7. HIGHER-ORDER FUNCTIONS
function calculator(operation, a, b) {
  return operation(a, b);
}

const multiply = (x, y) => x * y;
calculator(multiply, 4, 5); // 20

// 8. CLOSURES
function createCounter() {
  let count = 0;
  return function() {
    count++;
    return count;
  };
}

const counter = createCounter();
counter(); // 1
counter(); // 2

// 9. RECURSION
function fibonacci(n) {
  if (n <= 1) return n;
  return fibonacci(n - 1) + fibonacci(n - 2);
}

fibonacci(6); // 8

// 10. FUNCTION PROPERTIES
function greetUser(name) {
  greetUser.callCount = (greetUser.callCount || 0) + 1;
  return `Hello, ${name}! (Called ${greetUser.callCount} times)`;
}

greetUser("Alice"); // "Hello, Alice! (Called 1 times)"
greetUser("Bob");   // "Hello, Bob! (Called 2 times)"
        
      

Explanation

JavaScript soporta múltiples formas de definir funciones. Las funciones flecha proporcionan sintaxis concisa y enlace léxico de this.

Common Use Cases

  • Reutilización de código
  • Manejo de eventos
  • Llamadas a API

Related JavaScript Syntax

Master Funciones in JavaScript

Understanding funciones is fundamental to writing clean and efficient JavaScript code. This comprehensive guide provides you with practical examples and detailed explanations to help you master this important concept.

Whether you're a beginner learning the basics or an experienced developer looking to refresh your knowledge, our examples cover real-world scenarios and best practices for using funciones effectively in your JavaScript projects.

Key Takeaways

  • Reutilización de código
  • Manejo de eventos
  • Llamadas a API