Callback Functions:
===================
-> Callback function is a function that is passed as an argument to another function and is executed after the completion of that function.
-> Callbacks are a fundamental concept in asynchronous programming and are used to ensure that code runs in non-blocking way.

Syntax:
=======
function f1(f2){
}

function f2(){
}

function greets(name){
    console.log("Hello",name);
}

function processUserInput(callback){
    const name = "Kishore";
    callback(name);
}

 processUserInput(greets);

Use cases of callback functions:
================================
1) Asynchronous operations
==========================
	API Calls
	File reading/writing etc.
2) Event Handling
====================================================
Promises:
=========
-> Promises are powerful way to handle asynchronous operations.
-> A promise is an object that represents the eventual completion of an Asynchronous operation and its resulting a value.
-> Each promise can define with three different states:
	1) Pending: Initial state, neither fulfilled nor rejected.
	2) Fulfilled: The operation is completed successfully.
	3) Rejected: The Operation failed.

Creating of Promise:
====================
constructor
	Promise()
Syntax:
	Any Object name = new Promise((resolve, reject) => {});

let promise = new Promise((resolve, reject) => {
    let condition = true;
    
    if(condition){
        resolve("Promise is fulfilled.");
    }
    else{
        reject("Promise if rejected.");
    }
});

===================
Handling with promise:
======================

let fetchData = new Promise((resolve,reject) => {
    let success = true;
    
    setTimeout(() => {
        if(success){
            resolve("Data fetched successfully.");
        }
        else{
            reject("Failed to fetch data.");
        }
    },2000);
});

fetchData
    .then((data) => {
        console.log(data);
    })
    .catch((error) => {
        console.log(error);
    });

chaining promises:
==================
-> a promise is associated with a value, that value can send to another promise is called as "Chaining promise".

let promiseChain = new Promise((resolve,reject) => {
    resolve(100);
});

promiseChain
    .then((value) => {
        console.log(value); // 100
        return value * 2; // 200
    })
    .then((value) => {
        console.log(value); // 200
        return value * 3; // 600
    })
    .then((value) => {
        console.log(value); // 600
    })
    .catch((error) => {
        console.log("Error: "+error);
    });