What is a promise and what are its states?

A Promise is an object representing the eventual completion (or failure) of an asynchronous operation and its resulting value.

A promise can be in one of three states:

• Pending: The initial state, not yet fulfilled or rejected.
• Fulfilled: The operation completed successfully. In this state, the promise has a resulting value.
• Rejected: The operation failed with an error. In this state, the promise has a reason for rejection (an error).

Once a promise transitions to either Fulfilled or Rejected, it is considered settled. The state of a settled promise cannot change.