方法一：FileReader()

<input type="file" id="fileInput" />

<script>
  const fileInput = document.getElementById('fileInput')
  fileInput.addEventListener('change', function (e) {
    const file = e.target.files[0]
    const reader = new FileReader()
    reader.onload = function (event) {
      const text = event.target.result
      console.log(text)
    }
    reader.readAsText(file, 'GB2312')
  })
</script>

方法二：fetch()

<input type="file" id="fileInput" />

<script>
  const fileInput = document.getElementById('fileInput')
  fileInput.addEventListener('change', function (e) {
    const file = e.target.files[0]
    fetch(file)
    .then((res) => res.arrayBuffer())
    .then((fileContent) => {
      const decoder = new TextDecoder('GB2312')
      const text = decoder.decode(fileContent)
      console.log(text)
    })
    .catch((error) => {
      console.log(error)
    })
  })
</script>

相关URL方法

URL.createObjectURL('文件') 可以输出一个文件的临时url

let file_path = URL.createObjectURL('文件')