let promise = new Promise(function(resolve, reject) {
      setTimeout(() => reject(new Error("Whoops!")), 1000);
});

// reject runs the second function in .then
promise.then(
  result => alert(result), // doesn't run
  error => alert(error) // shows "Error: Whoops!" after 1 second
);

let promise = new Promise(function(resolve, reject) {
      setTimeout(() => reject(new Error("Whoops!")), 1000);
});

// reject runs the second function in .then
promise.then(
  result => alert(result), // doesn't run
  error => alert(error) // shows "Error: Whoops!" after 1 second
);

In the above code snippets even though I am calling reject but promise state is ing as resolved but when I am removing error => alert(error) from promise.then then I am getting promise state as rejected If one is calling reject then promise state should be rejected not resolved am I correct?

• javascript
• ecmascript-6
• promise
• es6-promise

Share Improve this question Follow edited Nov 14, 2018 at 11:47 Hassan Imam 22.6k66 gold badges4545 silver badges5353 bronze badges asked Nov 14, 2018 at 11:45 Alex_AngularAlex_Angular 10711 silver badge66 bronze badges

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4 Answers 4

Sorted by: Reset to default 2

The promise that is resolved is not the original promise, but the promise returned by then. The original promise is indeed rejected, and you can verify that by console.log(promise). But because you chained then it returns another promise ..

Return value [of then]

A Promise in the pending status. The handler function (onFulfilled or onRejected) then gets called asynchronously (as soon as the stack is empty). After the invocation of the handler function, if the handler function:

• returns a value, the promise returned by then gets resolved with the returned value as its value;
• doesn't return anything, the promise returned by then gets resolved with an undefined value;
• throws an error, the promise returned by then gets rejected with the thrown error as its value;

...

This second point is what applies to your case. You can verify that by observing that Promise.reject().then(undefined, ()=>{})
returns a promise that gets resolved with an undefined value.

You can also handle Promises in "then-catch" fashion like below

let promise = new Promise(function(resolve, reject) {
  setTimeout(() => reject('Error'));
});

promise
  .then(result => console.log('Result ', result)) 
  .catch(error => console.log('This is Error message -', error))

The final status of the promise is also rejected in your case. Try console.log(promise); It has nothing to do with error => alert(error)

The code you posted seems to work correctly both on Chrome and Firefox - the Promise was rejected as expected. reject function marks the Promise as rejected - you can then react upon that rejection either by passing a callback function into a second argument of then or by using the catch method. Both approaches are correct.

If you are encountering any unexpected behaviour, verify that you are not using some faulty polyfill that replaces the original Promise object.

Reference: Promise.prototype.then, Promise.prototype.catch