如何使用NodeJS express框架从MongoDB中搜索关键字(错误: MongoDB schema.index不是一个函数)

const mongoose = require('mongoose');
const Schema = mongoose.Schema;

const yourSchema = new Schema({
  keyword: {
    type: String,
    required: true
  }
});

yourSchema.index({ keyword: 'text' });

const YourModel = mongoose.model('YourModel', yourSchema);
module.exports = YourModel;

const YourModel = require('../models/yourModel');

router.get('/search', async (req, res) => {
  const keyword = req.query.keyword;
  try {
    const results = await YourModel.find({ $text: { $search: keyword } });
    res.json(results);
  } catch (error) {
    console.error(error);
    res.status(500).json({ message: 'Internal Server Error' });
  }
});