promises.js

//* Promises :
//? A Promise is an object representing the eventual completion or failure of an asynchronous operation and its resulting value. Promises are a way to handle asynchronous
//? A promise is an object that may produce a single value sometime in the future.
//? It has three states: pending, fulfilled (with data), and rejected (with error).

const myPromise = new Promise(function (res, rej) {
  setTimeout(function () {
    if (Math.random() < 0.9) {
      return res("Hooray!");
    }
    return rej("Oh no!");
  }, 1000);
});

myPromise
  .then(function (data) {
    console.log("Success: " + data);
  })
  .catch(function (err) {
    console.log("Error: " + err);
  });

//todo ==> If Math.random() returns less than 0.9 the following is logged:// "Success: Hooray!"// If Math.random() returns 0.9 or greater the following is logged:// "Error: On no!"

//todo  ==> A Promise is an object representing the eventual completion or failure of an asynchronous operation. Essentially, a promise is a returned object to which you attach callbacks, instead of passing callbacks into a function

//todo  ==> Promises resolve the issue of ‘callback hell’ which is nothing but a recursive structure of callbacks (callbacks within callbacks within callbacks and so forth).

const promise = new Promise((resolve, reject) => {
  isNameExist = false;
  if (isNameExist) {
    resolve("User name exist");
  } else {
    reject("error");
  }
});
promise
  .then((result) => console.log(result))
  .catch((error) => {
    console.log(error);
  });