JavaScript Functions Higher-Order, Anonymous, Invoked & More!

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JavaScript functions are a cornerstone of modern web development, offering a way to organize, reuse, and execute code efficiently. This guide provides a detailed overview of the various types of functions in JavaScript, complete with examples.

1. Normal Function
A named function that can be called anywhere in its scope.

Syntax:

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

Example:

function greet(name) {
    return `Hello, ${name}!`;
}
console.log(greet("John")); // Output: Hello, John!

2. Function Expression
A function defined and assigned to a variable, usually anonymous.
Syntax:

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

Example:

const add = function(a, b) {
    return a + b;
};
console.log(add(5, 3)); // Output: 8

3. Arrow Function
A concise syntax for writing functions introduced in ES6. Arrow functions do not have their own this.
Syntax:

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

Example:

const multiply = (a, b) => a * b;
console.log(multiply(4, 5)); // Output: 20

4. Immediately Invoked Function Expression (IIFE)
A function that is executed immediately after it is defined.
Syntax:

(function() {
    // Function body
})();

Example:

(function() {
    console.log("IIFE executed!");
})(); // Output: IIFE executed!

5. Constructor Function
A special function used to create and initialize objects.
Syntax:

function ConstructorFunction(parameters) {
    this.property = value;
}

Example:

function Person(name, age) {
    this.name = name;
    this.age = age;
}
const person1 = new Person("Alice", 30);
console.log(person1.name); // Output: Alice

6. Class Method
A function defined inside a class to operate on class properties.
Syntax:

class ClassName {
    methodName(parameters) {
        // Method body
    }
}

Example:

class Calculator {
    add(a, b) {
        return a + b;
    }
}
const calc = new Calculator();
console.log(calc.add(7, 8)); // Output: 15

7. Generator Function
A function that can pause and resume execution using the yield keyword.
Syntax:

function* generatorFunction() {
    yield value;
}

Example:

function* countUpToThree() {
    yield 1;
    yield 2;
    yield 3;
}
const counter = countUpToThree();
console.log(counter.next().value); // Output: 1
console.log(counter.next().value); // Output: 2
console.log(counter.next().value); // Output: 3

8. Async Function
A function that works with asynchronous operations, using asyncand await.
Syntax:

async function functionName(parameters) {
    // Function body
}

Example:

async function fetchData() {
    const response = await fetch("https://api.example.com/data");
    const data = await response.json();
    return data;
}
fetchData().then(console.log);

9. Recursive Function
A function that calls itself to solve a smaller subproblem.
Syntax:

function functionName(parameters) {
    if (baseCondition) return result;
    return functionName(smallerProblem);
}

Example:

function factorial(n) {
    if (n === 0) return 1;
    return n * factorial(n - 1);
}
console.log(factorial(5)); // Output: 120

10. Anonymous Function
A function without a name, often used as a callback or inside expressions.
Syntax:

(function() {
    // Function body
})();

Example:

const numbers = [1, 2, 3];
numbers.forEach(function(number) {
    console.log(number);
});
// Output: 1, 2, 3

11. Higher-Order Function
A function that accepts another function as an argument or returns a function.
Syntax:

function higherOrderFunction(callback) {
    return callback();
}

Example:

function greet() {
    return "Hello, world!";
}
function executeFunction(fn) {
    console.log(fn());
}
executeFunction(greet); // Output: Hello, world!