在返回所有值之前，我如何等待所有承诺解决？

Question

我正在使用 bluebird 的 Promise.map。在调度包含对象数组的事件之前，我试图等待所有承诺都解决。

readFiles() {
    const fileArray = Array.from(this.fileSelectInput.files)
    const promises = []

    window.Promise.map(fileArray, (file, index) => {
      return window.jsmediatags.read(file, {
        onSuccess: tag => {
          promises.push({
            id: index + 1,
            title: tag.tags.title || undefined,
            artist: tag.tags.artist || undefined
          })
          promises.sort((a, b) => a.id - b.id)
          console.log('I should be first')
        }
      })
    }).then(() => {
        console.log('I should be second')
        this.dispatchEvent(new CustomEvent('tracks-selected', {
          detail: promises
        }))
      }
    }

我运行遇到 I should be second 在 I should be first 之前打印到控制台的问题。事件调度的 detail: promises 包含一个空数组。

Answer 1

您可能正在寻找

const fileArray = Array.from(this.fileSelectInput.files);

window.Promise.map(fileArray, file => {
  return new Promise((resolve, reject) => {
    window.jsmediatags.read(file, {
      onSuccess: resolve,
      // also pass reject as an error handler if jsmediatags supports that
    });
  });
}).then(tags => {
  const results = tags.map(tag => ({
    id: index + 1,
    title: tag.tags.title || undefined,
    artist: tag.tags.artist || undefined
  }));
  // results.sort((a, b) => a.id - b.id) - not necessary given .map() keeps the order
  this.dispatchEvent(new CustomEvent('tracks-selected', {
    detail: results
  }))
});

在返回所有值之前，我如何等待所有承诺解决？

How can I wait for all promises to resolve before returning all their values?

javascript

promise

bluebird