如何成功等待FileReader.onload加载文件？

Question

我要做的就是只需通过循环阅读多个文件信息即可。但是，即使我使用了Promise，JavaScript也不会等待FileReader.onload。

我们如何等待filereader.onload？这是代码示例。

    const promises = [];
    for (let i = 0; i < files.length; i++) {
      promises.push(
        new Promise((resolve, reject) => {
          const fileReader = new FileReader();
          const filename = files[i].object.name;

          audioDict.filename[i] = filename;
          fileReader.readAsArrayBuffer(files[i].object);
          fileReader.onload = function (e: any) {
            audioCtx
              .decodeAudioData(e.target.result)
              .then(function (decodedData: AudioBuffer) {
                // source.buffer = decodedData;

                audioDict.audio[i] = {};
                for (let c = 0; c < decodedData.numberOfChannels; c++) {
                  audioDict.audio[i][c] = decodedData.getChannelData(c);
                }
                audioDict.sr[i] = decodedData.sampleRate;
              });
          };
          resolve(audioDict);
        })
      );
    }

    Promise.all(promises).then(() => {
      // Do something using audioDict here.
      console.log("done!");
    });

Answer 1

我想在Onload功能中移动您的分辨率函数调用将解决此问题。

const promises = [];
for (let i = 0; i < files.length; i++) {
  promises.push(
    new Promise((resolve, reject) => {
      const fileReader = new FileReader();
      const filename = files[i].object.name;

      audioDict.filename[i] = filename;
      fileReader.readAsArrayBuffer(files[i].object);
      fileReader.onload = function (e: any) {
        audioCtx
          .decodeAudioData(e.target.result)
          .then(function (decodedData: AudioBuffer) {
            // source.buffer = decodedData;

            audioDict.audio[i] = {};
            for (let c = 0; c < decodedData.numberOfChannels; c++) {
              audioDict.audio[i][c] = decodedData.getChannelData(c);
            }
            audioDict.sr[i] = decodedData.sampleRate;
            resolve(audioDict);
          });
      };
    })
  );
}

Promise.all(promises).then(() => {
  // Do something using audioDict here.
  console.log("done!");
});