Callback, Promise and Async / Await

callback_promise_asyncAwait.js

// Callbacks
function user(callback1){
    let name = 'Gaurav';
    setTimeout(()=> {
          callback1(name); // if callback not take argument give undefined
    }, 2000);
}

function userAge(name, callback2){
    let age = name + ' age is 24.';
      setTimeout(()=> {
          callback2(age);
    }, 2000);
}

// callback runs from here
user((name) => {
    console.log(name) // If 1st dn not pass name in callback1(name) >>> it print undefined;
    return userAge(name, (age) => {
        console.log(`${age}`)
    });
});



// Promise 
function userPromise(){  // parent scope
    let name = 'Gaurav';
    return new Promise((resolve, reject) => { // parent
          setTimeout(()=> { 
          resolve(name); // lexical scope parent ka scope
    }, 2000);
    })
}

function userAgePromise(name){
    let age = name + ' age is 24.';
    return new Promise((resolve, reject) => { // parent
          setTimeout(()=> { 
          resolve(age); // lexical scope parent ka scope
    }, 2000);
    })
}

// Promise chain then . catch .finally
// 1. >> 
    userPromise().then((name) => userAgePromise(name)).then((age) => console.log(age)).catch((err) => console.log(err)).finally(() => console.log('finally completed'));

//  2. >> 
    userPromise().then((name) => {
               console.log(name);
               return userAgePromise(name);
                 }).then((age) => {
                   console.log(age);
                     }).catch((err) => {
                       console.log(`Error Happened: ${age}`);
                        }).finally(() => { 
                           console.log('Finaly reached end of promise page')
                             });



// Async / Await
async function asyncCodeUser(){
    const name = await userPromise();
    console.log(name);
    
    const age = await userAgePromise(name);
    console.log(age);
};