使用spark-md5获取文件md5值

网上搜到的文章都乱七八糟的，参照官方例子稍微改了改

function md5WithChunk(file, chunkSize, processCallback = console.log) {
  return new Promise((resolve, reject) => {
    const blobSlice =
      File.prototype.slice ||
      File.prototype.mozSlice ||
      File.prototype.webkitSlice
    let chunks = Math.ceil(file.size / chunkSize)
    let currentChunk = 0
    let spark = new SparkMD5.ArrayBuffer()
    let fileReader = new FileReader()
    fileReader.onerror = reject
    fileReader.onload = (e) => {
      processCallback(currentChunk / chunks)
      spark.append(e.target.result)
      currentChunk++
      if (currentChunk < chunks) {
        loadNext()
      } else {
        resolve(spark.end())
      }
    }
    function loadNext() {
      let start = currentChunk * chunkSize
      let end = start + chunkSize >= file.size ? file.size : start + chunkSize
      fileReader.readAsArrayBuffer(blobSlice.call(file, start, end))
    }
    loadNext()
  })
}

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