Promises are used to handle asynchronous operations in javascript. The Promise object represents the eventual completion (or failure) of an asynchronous operation and its resulting value. A Promise is in one of these states: pending: initial state, neither fulfilled nor rejected. fulfilled: meaning that the operation was completed successfully. rejected: meaning that the operation failed. let promise = new Promise(function (resolve, reject) { const x = "abc"; const y = "abc" if (x === y) { resolve(); } else { reject(); } }); promise. then(function () { console.log('Success, You are a GEEK'); }). catch(function () { console.log('Some error has occurred'); }); The then method is called when the promise is fulfilled. It takes a function as an argument, which will run when the promise is successful. The catch method is called when the promise is rejected. It also takes a function, which will run if there’s an error.