The finally()
method returns a Promise
. When the promise is settled, i.e either fulfilled or rejected, the specified callback function is executed. This provides a way for code to be run whether the promise was fulfilled successfully or rejected once the Promise
has been dealt with.
This helps to avoid duplicating code in both the promise's then()
and catch()
handlers.
Syntax
p.finally(onFinally); p.finally(function() { // settled (fulfilled or rejected) });
Parameters
onFinally
- A
Function
called when thePromise
is settled.
Return value
Returns a Promise
whose finally
handler is set to the specified function, onFinally
.
Description
The finally()
method can be useful if you want to do some processing or cleanup once the promise is settled, regardless of its outcome.
The finally()
method is very similar to calling .then(onFinally, onFinally)
however there are a couple of differences:
- When creating a function inline, you can pass it once, instead of being forced to either declare it twice, or create a variable for it
- A
finally
callback will not receive any argument, since there's no reliable means of determining if the promise was fulfilled or rejected. This use case is for precisely when you do not care about the rejection reason, or the fulfillment value, and so there's no need to provide it. So for example:- Unlike
Promise.resolve(2).then(() => {}, () => {})
(which will be resolved withundefined
),Promise.resolve(2).finally(() => {})
will be resolved with2
. - Similarly, unlike
Promise.reject(3).then(() => {}, () => {})
(which will be fulfilled withundefined
),Promise.reject(3).finally(() => {})
will be rejected with3
.
- Unlike
Note: A throw
(or returning a rejected promise) in the finally
callback will reject the new promise with the rejection reason specified when calling throw
.
Examples
Using finally
let isLoading = true; fetch(myRequest).then(function(response) { var contentType = response.headers.get("content-type"); if(contentType && contentType.includes("application/json")) { return response.json(); } throw new TypeError("Oops, we haven't got JSON!"); }) .then(function(json) { /* process your JSON further */ }) .catch(function(error) { console.error(error); /* this line can also throw, e.g. when console = {} */ }) .finally(function() { isLoading = false; });
Please do not add polyfills on MDN pages. For more details, refer to: https://discourse.mozilla.org/t/mdn-rfc-001-mdn-wiki-pages-shouldnt-be-a-distributor-of-polyfills/24500
Specifications
Specification |
---|
ECMAScript (ECMA-262) The definition of 'Promise.prototype.finally' in that specification. |
Browser compatibility
To contribute to this compatibility data, please write a pull request against this repository: https://github.com/mdn/browser-compat-data.
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
finally() | Chrome Full support 63 | Edge Full support 18 | Firefox Full support 58 | IE No support No | Opera Full support 50 | Safari Full support 11.1 | WebView Android Full support 63 | Chrome Android Full support 63 | Firefox Android Full support 58 | Opera Android Full support 46 | Safari iOS Full support 11.3 | Samsung Internet Android Full support 8.0 | nodejs Full support 10.0.0 |
Legend
- Full support
- Full support
- No support
- No support