var xhr = new XMLHttpRequest();
var startTime, endTime;

xhr.onreadystatechange = function() {
    if (xhr.readyState === 1) { // OPENED
        startTime = new Date().getTime();
    } else if (xhr.readyState === 4) { // DONE
        endTime = new Date().getTime();
        var duration = endTime - startTime;
        console.log('请求持续时间: ' + duration + 'ms');
    }
};

xhr.open('GET', 'https://api.example.com/data', true);
xhr.send();

const startTime = performance.now();

fetch('https://api.example.com/data')
    .then(response => {
        const endTime = performance.now();
        const duration = endTime - startTime;
        console.log(`请求持续时间: ${duration}ms`);
        return response.json();
    })
    .catch(error => console.error('Error:', error));

// 发起请求前
performance.mark('ajaxStart');

fetch('https://api.example.com/data')
    .then(response => {
        performance.mark('ajaxEnd');
        performance.measure('ajaxDuration', 'ajaxStart', 'ajaxEnd');
        
        const measures = performance.getEntriesByName('ajaxDuration');
        console.log(`请求持续时间: ${measures[0].duration}ms`);
        
        // 清理性能条目
        performance.clearMarks();
        performance.clearMeasures();
        return response.json();
    });