<div id="container">
    <input type="file" id="fileInput" multiple="multiple">
</div>

let fileInput = document.querySelector('#fileInput')
const handleFileSelect = () => {
  const sizes = ['Bytes', 'KB', 'MB', 'GB']
  console.log(fileInput.files)
  const bytes = fileInput.files[0].size
  const k = 1024
  const i = Math.floor(Math.log(bytes) / Math.log(k)) // 为了算单位
  // Math.pow(k, i) k的i次方 这个大小对应Bytes, KB, MB, GB
  let fileSize = parseFloat((bytes / Math.pow(k, i)).toFixed(2)) + ' ' + sizes[i];
    console.log('文件大小:', fileSize)
  }
 fileInput.addEventListener('change', handleFileSelect);
 console.log(fileInput.files)