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如何添加多边形填充以支持Edge中的finally()?

finally polyfills promise javascript

5

Craig · 技术社区 · 8 年前

1 回复 | 直到 8 年前

1

21

Patrick Roberts Benjamin Gruenbaum 6 年前

这将处理该表的 species 除以下详细说明的行为外:

Promise.prototype.finally = Promise.prototype.finally || {
  finally (fn) {
    const onFinally = callback => Promise.resolve(fn()).then(callback);
    return this.then(
      result => onFinally(() => result),
      reason => onFinally(() => Promise.reject(reason))
    );
  }
}.finally;

finally() 取决于 then() 符合规范要求:

A. finally 回调将不会收到任何参数,因为没有可靠的方法来确定承诺是履行了还是拒绝了。这个用例正好适用于您不关心拒绝原因或履行价值的情况,因此不需要提供它。

不像 Promise.resolve(2).then(() => {}, () => {}) undefined ), Promise.resolve(2).finally(() => {}) 将通过以下方式解决: 2 .

类似地,不像 Promise.reject(3).then(() => {}, () => {}) (这将以 未定义 ), Promise.reject(3).finally(() => {}) 将被拒绝与 3 .

A. throw 最后 throw() .

当然,这是一个等价行为的演示:

const logger = (label, start = Date.now()) => (...values) => {
  console.log(label, ...values, `after ${Date.now() - start}ms`);
};

const delay = (value, ms) => new Promise(resolve => {
  setTimeout(resolve, ms, value);
});

// run test on native implementation
test('native');

// force Promise to use the polyfill implementation
Promise.prototype.finally = /* Promise.prototype.finally || */ {
  finally (fn) {
    const onFinally = callback => Promise.resolve(fn()).then(callback);
    return this.then(
      result => onFinally(() => result),
      reason => onFinally(() => Promise.reject(reason))
    );
  }
}.finally;

// run test on polyfill implementation
test('polyfill');

function test (impl) {
  const log = ordinal => state => logger(`${ordinal} ${impl} ${state}`);
  const first = log('first');

  // test propagation of resolved value
  delay(2, 1000)
    .finally(first('settled'))
    .then(first('fulfilled'), first('rejected'));

  const second = log('second');

  // test propagation of rejected value
  delay(Promise.reject(3), 2000)
    .finally(second('settled'))
    .then(second('fulfilled'), second('rejected'));

  const third = log('third');

  // test adoption of resolved promise
  delay(4, 3000)
    .finally(third('settled'))
    .finally(() => delay(6, 500))
    .then(third('fulfilled'), third('rejected'));

  const fourth = log('fourth');

  // test adoption of rejected promise
  delay(5, 4000)
    .finally(fourth('settled'))
    .finally(() => delay(Promise.reject(7), 500))
    .then(fourth('fulfilled'), fourth('rejected'));
}

.as-console-wrapper{max-height:100%!important}

幸亏 @Bergi his implementation 如果你觉得这篇文章有帮助的话,也可以投票。