Understanding Promises in JavaScript : asynchronous behaviour of Javascript Part -2

In the previous article, we learned about using callback for performing asynchronous operations. In ES06/ES2015, Javascript introduced something called Promises which helps you handle  asynchronous operations in a better way The Promise object represents the eventual completion (or failure) of an asynchronous operation and its resulting value. Promises provide a better way for managing asynchronous operations when compared to traditional callback-based way. Promises represent data that may not be available but will be available later upon completing some asynchronous operation. A promise can be called a placeholder for future data and  has 3 states PENDING RESOLVED REJECTED Immediately on creation, the state of a Promise is pending. Resolved state means the asynchronous operation is fulfilled. Rejected means that the asynchronous operation is not completed and has some errors. Many Javascript native apis for asynchronous operations support promises since ES06. Prior to that many libraries including JQuery and Bluebird were used to create promises for doing asynchronous operations. Example for promises JavaScript fetch method returns a promise.

You can see that immediately the state of promise is pending. Now for resolving the promise and getting the output Promise.prototype.then() and Promise.prototype.catch() Promise.prototype.then() and Promise.prototype.catch() The promise object has a then method that returns the promise…

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