Promise in Js

app.js

// Promises are different then events in these ways-

// 1- They are called only once.
// 2- we can have simple chaining then nested and complex chaining.
// 3- They are wrapped in try catch block
// 4- If a promise return any value , that itself becomes then-able.
// 5- Promise can be handled once it is already settled unlike eventHandlers we can't handle an event before setting eventHandlers.