In this tutorial, we will see details of Promise


  • Promise in JavaScript is an object that represents the eventual result of an asynchronous operation.
  • It provides a way to register callbacks to be notified when the operation completes, or when an error occurs.
  • Promise can be in one of three states:
    • pending
    • fulfilled
    • rejected.
  • When a Promise is created, it’s in a pending state, and then becomes either fulfilled when the operation succeeds, or rejected when the operation fails.

Example of Promise to handle the result of an asynchronous operation:

function getData() {
  return new Promise(function(resolve, reject) {
    // Perform an asynchronous operation
    setTimeout(function() {
      resolve("Data retrieved successfully");
    }, 1000);

  .then(function(result) {
  .catch(function(error) {

In this example, the getData function returns a Promise. The then method is used to register a callback that will be invoked when the Promise is fulfilled. The catch method is used to register a callback that will be invoked if the Promise is rejected.

When the getData function is called, it returns a Promise that represents the result of the asynchronous operation. The call to getData returns immediately, and the actual result of the operation will be available later, when the Promise is fulfilled. The callbacks registered with the then and catch methods will be invoked at the appropriate time, when the Promise is fulfilled or rejected.

Promises provide a clean and elegant way to handle asynchronous operations, as compared to traditional approaches such as callbacks, and make it easier to reason about and manage the flow of data in an asynchronous environment.

Thanks for Reading…