使用Ajax和HTML5实现文件上传功能

<form id="uploadForm" enctype="multipart/form-data">
  <input type="file" id="fileInput" name="file">
  <input type="button" value="上传" onclick="uploadFile()">
</form>

function uploadFile() {
  var fileInput = document.getElementById('fileInput');
  var file = fileInput.files[0];
  var formData = new FormData();

  formData.append('file', file);

  var xhr = new XMLHttpRequest();
  xhr.open('POST', 'upload.php', true);

  xhr.onload = function() {
    if (xhr.status === 200) {
      // 上传成功
      console.log(xhr.responseText);
    } else {
      // 上传失败
      console.error(xhr.statusText);
    }
  };

  xhr.send(formData);
}

<?php
$file = $_FILES['file'];

// 处理文件上传逻辑...

echo '文件上传成功';
?>