Types of Functions in JavaScript with Examples
JavaScript supports various types of functions, each serving different purposes. Let’s go through them one by one with examples.
1. Named Function
A named function has a specified name and can be reused.
🔹 Best used for code reusability.
function greet() {
   console.log("Hello, World!");
}
greet(); // Output: Hello, World!2. Anonymous Function
A function without a name, usually assigned to a variable.
🔹 Best used in callbacks and event listeners.
const greet = function() {
   console.log("Hello, Anonymous!");
};
greet(); // Output: Hello, Anonymous!3. Arrow Function (ES6)
A concise way to write functions using =>.
🔹 Best for short functions, callbacks, and this binding.
const add = (a, b) => a + b;
console.log(add(5, 3)); // Output: 8âš¡ Short Syntax Variants:
✅ Single Parameter:
const square = x => x * x;
console.log(square(4)); // Output: 16✅ No Parameters:
const sayHello = () => console.log("Hello!");
sayHello(); // Output: Hello!4. Immediately Invoked Function Expression (IIFE)
A function that runs immediately after being defined.
🔹 Best for preventing variable pollution in the global scope.
(function() {
   console.log("This runs immediately!");
})(); // Output: This runs immediately!🔹 Arrow function version:
(() => console.log("IIFE with Arrow Function!"))();
// Output: IIFE with Arrow Function!5. Generator Function (function*)
A function that can pause execution and resume later using yield.
🔹 Best for handling asynchronous operations & infinite sequences.
function* generateNumbers() {
   yield 1;
   yield 2;
   yield 3;
}
const gen = generateNumbers();
console.log(gen.next().value); // Output: 1
console.log(gen.next().value); // Output: 2
console.log(gen.next().value); // Output: 36. Higher-Order Function
A function that takes another function as an argument or returns a function.
🔹 Best for functional programming, callbacks, and composition.
function operate(x, y, operation) {
   return operation(x, y);
}
const multiply = (a, b) => a * b;
console.log(operate(3, 4, multiply)); // Output: 127. Recursive Function
A function that calls itself to solve a problem.
🔹 Best for problems like factorial, Fibonacci, and tree traversal.
function factorial(n) {
   return n === 0 ? 1 : n * factorial(n - 1);
}
console.log(factorial(5)); // Output: 1208. Callback Function
A function passed as an argument to another function.
🔹 Best for asynchronous tasks and event handling.
function greet(name, callback) {
   console.log("Hello, " + name);
   callback();
}
greet("John", () => console.log("Callback executed!"));
/*
Output:
Hello, John
Callback executed!
*/9. Pure Function
A function that always returns the same output for the same input and has no side effects.
🔹 Best for predictable results and functional programming.
function add(a, b) {
   return a + b;
}
console.log(add(2, 3)); // Output: 510. Async Function (async/await)
A function that works asynchronously using the await keyword.
🔹 Best for handling Promises and asynchronous operations.
async function fetchData() {
   let response = await fetch('https://jsonplaceholder.typicode.com/todos/1');
   let data = await response.json();
   console.log(data);
}
fetchData();Comparison Table: Function Types in JavaScript
| Function Type | Syntax | Use Case |
| Named Function | function myFunc() {} | Code reusability |
| Anonymous Function | const func = function() {} | Assigning functions to variables |
| Arrow Function | const func = () => {} | Shorter syntax, this binding |
| IIFE | (function() {})(); | Avoid global scope pollution |
| Generator Function | function* gen() { yield x; } | Pausable function execution |
| Higher-Order Function | function func(f) { f(); } | Functional programming |
| Recursive Function | function fact(n) { return n * fact(n-1); } | Problems like factorial, Fibonacci |
| Callback Function | function myFunc(cb) { cb(); } | Asynchronous tasks |
| Pure Function | function sum(a, b) { return a + b; } | Predictable results |
| Async Function | async function() { await task(); } | Handling Promises |
Conclusion
JavaScript provides multiple types of functions for different scenarios.
💡 Use Case Suggestions:
- Use named functions for readability.
- Use arrow functions for concise code.
- Use IIFE to avoid polluting the global scope.
- Use async/await for asynchronous operations.
- Use higher-order functions for better function composition.
