Node.js Q & A


What are Promises in Node.js?

Promises are a core feature introduced in ECMAScript 2015 (ES6) and widely adopted in Node.js for handling asynchronous operations. A Promise represents the eventual completion or failure of an asynchronous operation and allows you to write asynchronous code in a more structured and manageable way.


In Node.js, a Promise can be in one of three states:

  • Pending: The initial state of a Promise before the asynchronous operation is completed or rejected.
  • Fulfilled: The state of a Promise when the asynchronous operation is successfully completed.
  • Rejected: The state of a Promise when the asynchronous operation encounters an error or is rejected.


Promises have two primary methods:

  • then(): The then() method is used to handle the result of a Promise when it is fulfilled. It takes two optional callback functions: one for handling the fulfillment (resolve) and another for handling the rejection (reject).
  • catch(): The catch() method is used to handle errors or rejections that occur during the execution of a Promise. It is a shorthand for handling errors in the then() method’s second callback function.


Promises allow you to chain asynchronous operations together using the then() method, making it easier to write and reason about asynchronous code. They also provide better error handling capabilities compared to traditional callback-based approaches.

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