What happens if you don’t resolve or reject a promise?

by

A promise is just an object with properties in Javascript. There’s no magic to it. So failing to resolve or reject a promise just fails to ever change the state from “pending” to anything else. This doesn’t cause any fundamental problem in Javascript because a promise is just a regular Javascript object. The promise will still get garbage collected (even if still pending) if no code keeps a reference to the promise.

The real consequence here is what does that mean to the consumer of the promise if its state is never changed? Any .then() or .catch() listeners for resolve or reject transitions will never get called. Most code that uses promises expects them to resolve or reject at some point in the future (that’s why promises are used in the first place). If they don’t, then that code generally never gets to finish its work.

Or if code is using await on the promise instead of .then(), then that function will just remain suspended forever on that await. The rest of the function will be dead code and will never execute.

It’s possible that you could have some other code that finishes the work for that task and the promise is just abandoned without ever doing its thing. There’s no internal problem in Javascript if you do it that way, but it is not how promises were designed to work and is generally not how the consumer of promises expect them to work.

As you can see if the status is 401, I am redirecting to login page.
Promise is neither resolved nor rejected.

Is this code OK? Or is there any better way to accomplish this.

In this particular case, it’s all OK and a redirect is a somewhat special and unique case. A redirect to a new browser page will completely clear the current page state (including all Javascript state) so it’s perfectly fine to take a shortcut with the redirect and just leave other things unresolved. The system will completely reinitialize your Javascript state when the new page starts to load so any promises that were still pending will get cleaned up.

More Related Contents:

  1. How to return many Promises and wait for them all before doing other stuff
  2. ES6 promise settled callback?
  3. When is the body of a Promise executed?
  4. ES6 Promise.all() error handle – Is .settle() needed? [duplicate]
  5. Fulfill (don’t resolve) promise with another promise
  6. ES6 Promises – something like async.each?
  7. Filtering an array with a function that returns a promise
  8. Why is the response object from JavaScript fetch API a promise?
  9. Why does the Promise constructor require a function that calls ‘resolve’ when complete, but ‘then’ does not – it returns a value instead?
  10. What is the best general practice to timeout a function in promise [closed]
  11. When would someone need to create a deferred?
  12. ES6 promise execution order for returned values
  13. Promises, pass additional parameters to then chain
  14. How to extract data out of a Promise
  15. Are JavaScript forever-pending promises bad?
  16. Why does javascript ES6 Promises continue execution after a resolve?
  17. using await on global scope without async keyword
  18. ES6 Promise replacement of async.eachLimit / async.mapLimit
  19. Why does JavaScript Promise then handler run after other code?
  20. When is the body of a Promise constructor callback executed?
  21. ECMAScript 6 arrow function that returns an object
  22. One-liner to take some properties from object in ES 6
  23. Convert a string to a template string
  24. What is “function*” in JavaScript?
  25. Template literals syntax is not working in IE11
  26. ‘Access-Control-Allow-Credentials’ header in the response is ” which must be ‘true’
  27. Typescript: can not access member value in inherited class constructor
  28. JavaScript asynchronous programming: promises vs generators
  29. How to add mixins to ES6 javascript classes?
  30. ES6 arrow function and lexical scope inside a function [duplicate]

Leave a Comment