Description: The `Promise.prototype.finally` method is an addition to the Promise API in JavaScript that allows developers to add a handler that runs after a promise has been settled, regardless of its outcome. This method is particularly useful for performing cleanup tasks or executing code that should run regardless of the promise’s result, such as closing connections, releasing resources, or displaying final messages to the user. The syntax of `finally` is straightforward: it is invoked on a promise and takes a function as an argument, which will execute at the end of the promise’s lifecycle. This method does not take any arguments and does not affect the resolution value of the promise, meaning the value returned by the original promise remains intact. The introduction of `finally` enhances code readability and allows for cleaner promise handling, avoiding the need to duplicate code in `then` and `catch` blocks for common tasks that need to run at the end of the asynchronous process.
History: The `finally` method was introduced in the ECMAScript 2018 (ES9) specification, which was published in June 2018. Prior to its inclusion, developers often had to duplicate code in `then` and `catch` blocks to handle tasks that needed to run regardless of the promise’s outcome. The addition of `finally` was an important step in improving the ergonomics and readability of promise handling in JavaScript.
Uses: The `finally` method is primarily used in situations where cleanup or finalization code needs to be executed after an asynchronous operation has completed, regardless of whether it was successful or failed. This is common in operations involving external resources, such as database connections or network requests, where it is crucial to release resources or close connections properly.
Examples: A practical example of `finally` would be in a network request where a connection needs to be closed after receiving the response. For instance: `fetch(url).then(response => { /* handle response */ }).catch(error => { /* handle error */ }).finally(() => { /* close connection */ });`.
