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The finally() method returns a Promise. When the promise is settled, whether fulfilled or rejected, the specified callback function is executed. This provides a way for code that must be executed once the Promise has been dealt with to be run whether the promise was fulfilled successfully or rejected.

This lets you 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 the Promise 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 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.
  • Unlike Promise.resolve(2).then(() => {}, () => {}) (which will be resolved with undefined), Promise.resolve(2).finally(() => {}) will be resolved with 2.
  • Similarly, unlike Promise.reject(3).then(() => {}, () => {}) (which will be fulfilled with undefined), Promise.reject(3).finally(() => {}) will be rejected with 3.

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

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.log(error); })
  .finally(function() { isLoading = false; });

Specifications

Specification Status Comment
TC39 proposal Stage 4  

Browser compatibility

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidiOS SafariSamsung InternetNode.js
Basic supportChrome Full support 63Edge No support NoFirefox Full support 58IE No support NoOpera Full support 50Safari Full support 11.1WebView Android Full support 63Chrome Android Full support 63Edge Mobile No support NoFirefox Android Full support 58Opera Android Full support 50Safari iOS Full support 11.1Samsung Internet Android No support Nonodejs Full support 10.0.0

Legend

Full support  
Full support
No support  
No support

See also

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Colaboradores desta página: tuxpilgrim
Última atualização por: tuxpilgrim,