Promise.prototype.finally()

Метод finally() возвращает Promise. Когда Promise (обещание) был выполнен, в не зависимости успешно или с ошибкой, указаная функция будет выполнена. Это дает возможность запустить один раз определенный участок кода, который должен выполнится вне зависимости от того, с каким результатом выполнился Promise.

Это позволяет вам избавится от дубликации кода в обработчиках then() и catch().

Синтаксис

p.finally(onFinally);

p.finally(function() {
   // завершен (успешно или с ошибкой)
});

Параметры

onFinally

Функция Function вызываемая когда Promise (обещание) завершено.

Возвращаемое значение

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 resolved with undefined), Promise.reject(3).finally(() => {}) will be rejected with 3.

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

Browser compatibility

To contribute to this compatibility data, please write a pull request against this repository: https://github.com/mdn/browser-compat-data.

See also

• Promise
• Promise.prototype.then()
• Promise.prototype.catch()