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functions.js
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functions.js
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// 1. Function Basics:
// - Functions are reusable blocks of code that perform a specific task.
// - They help in organizing code, promoting reusability, and improving readability.
// - Functions can be defined using the `function` keyword or through function expressions.
// 2. Function Declaration:
// - A function declaration defines a named function with optional parameters.
// - It consists of the `function` keyword, followed by the function name, a list of parameters in parentheses, and the function body enclosed in curly braces.
function regularFunction(a, b) {
return a + b;
}
console.log(regularFunction(2, 3)); // Output: 5
// 3. Function Expression:
// - A function expression assigns a function to a variable or property.
// - It can be anonymous or have a name.
var multiply = function (a, b) {
return a * b;
};
const functionExpression = function (a, b) {
return a - b;
};
console.log(functionExpression(5, 3)); // Output: 2
// 4. Arrow Functions (ES6):
// - Arrow functions provide a concise syntax for writing functions.
// - They have a shorter syntax compared to regular functions.
var square = (x) => x * x;
console.log(square(2)); // Output: 4
// 5. IIFE (Immediately Invoked Function Expression):
// - An IIFE is a function that is executed immediately after it is defined.
// - It helps create a new scope, preventing variable collisions.
(function () {
console.log("IIFE executed!");
})();
// 6. Function Parameters:
// - Functions can accept parameters, which are placeholders for values passed to the function.
// - Parameters are listed in the function declaration or expression, separated by commas.
function greet(name) {
console.log("Hello, " + name + "!");
}
// 7. Default Parameters (ES6):
// - Default parameters allow you to specify default values for function parameters.
// - If a value is not passed for a parameter, the default value is used instead.
function greet(name = "Guest") {
console.log("Hello, " + name + "!");
}
// 8. Rest Parameters (ES6):
// - Rest parameters allow you to pass multiple arguments to a function as an array.
// - The rest parameter is prefixed with three dots (`...`).
function sum(...numbers) {
return numbers.reduce((total, num) => total + num, 0);
}
// 9. Return Statement:
// - The `return` statement specifies the value to be returned by a function.
// - It terminates the function execution and sends the value back to the caller.
function square(x) {
return x * x;
}
// 10. Callback Functions:
// - A callback function is a function passed as an argument to another function.
// - It allows asynchronous operations and is called when the task is complete.
function callbackFunction(callback) {
callback();
}
callbackFunction(function () {
console.log("Callback function executed!");
});
// 11. Higher-Order Functions:
// - Higher-order functions are functions that accept other functions as arguments or return functions.
// - They provide a powerful way to manipulate and abstract over functions.
function higherOrderFunction(callback) {
return callback(2, 3);
}
const addition = function (a, b) {
return a + b;
};
console.log(higherOrderFunction(addition)); // Output: 5
// 12. Recursive
// - Recursive functions are functions that call themselves.
// - They are useful for solving problems that can be divided into smaller, similar subproblems.
function factorial(n) {
if (n === 0 || n === 1) {
return 1;
} else {
return n * factorial(n - 1);
}
}
console.log(factorial(5)); // Output: 120
// 7. Closure
function outerFunction() {
const outerVariable = "I am from the outer function";
function innerFunction() {
console.log(outerVariable);
}
return innerFunction;
}
const closure = outerFunction();
closure(); // Output: I am from the outer function
// 10. Generator Function
function* generatorFunction() {
yield 1;
yield 2;
yield 3;
}
const generator = generatorFunction();
console.log(generator.next().value); // Output: 1
console.log(generator.next().value); // Output: 2
console.log(generator.next().value); // Output: 3
// 11. Promises and Async/Await:
// Promises and async/await are used for handling asynchronous operations.
// Promises allow you to handle the result of an asynchronous operation when it's available,
// while async/await provides a more synchronous-like way of writing asynchronous code.
function fetchData() {
return new Promise((resolve, reject) => {
// Simulating an asynchronous operation
setTimeout(() => {
const data = "Some data";
resolve(data);
}, 1000);
});
}
fetchData()
.then((data) => {
console.log(data); // Output: Some data
})
.catch((error) => {
console.log(error);
});
// Async/Await
async function fetchData() {
return new Promise((resolve, reject) => {
setTimeout(() => {
const data = "Some data";
resolve(data);
}, 1000);
});
}
async function getData() {
try {
const data = await fetchData();
console.log(data);
// Output: Some data
} catch (error) {
console.log(error);
}
}
getData();
// Higher-Order Functions and Function Composition
// Higher-order functions as I mentioned above and
// They are often used for function composition,
// which is the process of combining multiple functions to create a new function.
function add(a, b) {
return a + b;
}
function multiply(a, b) {
return a * b;
}
function compose(func1, func2) {
return function (a, b) {
return func2(func1(a, b), b);
};
}
const addAndMultiply = compose(add, multiply);
console.log(addAndMultiply(2, 3)); // Output: 10