Function Expression: A function can also be defined as an expression and assigned to a variable. This is called a function expression.

// Function expression
const multiply = function(a, b) {
  return a * b;
};

let product = multiply(4, 5);
console.log(product); // Output: 20

Function expressions are not hoisted in the same way as function declarations, meaning you must define them before you can call them.

Arrow Functions (ES6+): Arrow functions provide a more concise syntax for writing function expressions. They are especially useful for simple, one-line functions.

Basic Syntax: (param1, param2, ..., paramN) => expression (implicitly returns expression) Or for multiple statements: (param1, param2, ..., paramN) => { // statements return value; // Explicit return needed for multi-line blocks }

Examples:

// Traditional function expression
const addOld = function(a, b) {
  return a + b;
};

// Arrow function (concise body, implicit return)
const addArrow = (a, b) => a + b;

console.log(addArrow(3, 7)); // Output: 10

// Arrow function with multiple statements (explicit return)
const greetArrow = (name) => {
  let message = "Hello, " + name;
  return message;
};
console.log(greetArrow("Developer")); // Output: Hello, Developer

// Arrow function with no parameters
const sayHi = () => console.log("Hi!");
sayHi(); // Output: Hi!

// Arrow function with one parameter (parentheses optional)
const double = x => x * 2;
console.log(double(5)); // Output: 10

Key differences with traditional functions:

• this keyword binding: Arrow functions do not have their own this context. They inherit this from the surrounding (lexical) scope. This is a significant difference and often beneficial in callbacks and methods.
• No arguments object: Arrow functions do not have their own arguments object. You can use rest parameters (...args) instead.
• Cannot be used as constructors (cannot be called with new).