如何将多选列表传入变量？

<select multiple>
  <option value="option1">选项1</option>
  <option value="option2">选项2</option>
  <option value="option3">选项3</option>
</select>

var selectElement = document.querySelector('select');
var selectedOptions = [];
for (var i = 0; i < selectElement.options.length; i++) {
  if (selectElement.options[i].selected) {
    selectedOptions.push(selectElement.options[i].value);
  }
}

// 使用AJAX请求将选中的选项发送给服务器
var xhr = new XMLHttpRequest();
xhr.open('POST', '/your-backend-endpoint', true);
xhr.setRequestHeader('Content-Type', 'application/json');
xhr.send(JSON.stringify(selectedOptions));

// 或者将其作为表单数据提交
var form = document.querySelector('form');
var hiddenInput = document.createElement('input');
hiddenInput.type = 'hidden';
hiddenInput.name = 'selectedOptions';
hiddenInput.value = selectedOptions.join(',');
form.appendChild(hiddenInput);
form.submit();

# 使用Python和Flask框架的示例
from flask import Flask, request

app = Flask(__name__)

@app.route('/your-backend-endpoint', methods=['POST'])
def handle_selected_options():
    selected_options = request.get_json()
    # 在这里处理选中的选项
    return 'Success'

if __name__ == '__main__':
    app.run()