document.getElementById('calculateBtn').addEventListener('click', function(e) {
    e.preventDefault();
    
    // 获取输入值
    const height = parseFloat(document.getElementById('height').value);
    const weight = parseFloat(document.getElementById('weight').value);
    
    // 验证输入
    if (isNaN(height) || isNaN(weight) || height <= 0 || weight <= 0) {
        alert('请输入有效的身高和体重数值');
        return;
    }
    
    // 发送AJAX请求
    const xhr = new XMLHttpRequest();
    xhr.open('POST', '/calculate-bmi', true);
    xhr.setRequestHeader('Content-Type', 'application/json');
    
    xhr.onload = function() {
        if (xhr.status === 200) {
            try {
                const response = JSON.parse(xhr.responseText);
                document.getElementById('result').innerHTML = `您的BMI是: ${response.bmi.toFixed(2)}`;
            } catch (e) {
                console.error('解析响应失败:', e);
            }
        } else {
            console.error('请求失败:', xhr.status);
        }
    };
    
    xhr.onerror = function() {
        console.error('请求错误');
    };
    
    xhr.send(JSON.stringify({ height: height, weight: weight }));
});

const express = require('express');
const app = express();
const bodyParser = require('body-parser');

app.use(bodyParser.json());

app.post('/calculate-bmi', (req, res) => {
    const { height, weight } = req.body;
    
    if (!height || !weight || isNaN(height) || isNaN(weight)) {
        return res.status(400).json({ error: '无效的输入' });
    }
    
    const bmi = weight / Math.pow(height / 100, 2); // 假设身高以厘米为单位
    res.json({ bmi: bmi });
});

app.listen(3000, () => {
    console.log('服务器运行在3000端口');
});