Navigation Timing API：TTFB/DOMContentLoaded/load 分析

概述Navigation Timing v2 提供高精度的导航项，包含重定向、DNS/TCP/TLS、TTFB 与 DOM 加载与完成事件时间，用于端到端性能分析。用法/示例const nav = performance.getEntriesByType('navigation')[0] const ttfb = nav.responseStart - nav.requestStart const dcl = nav.domContentLoadedEventEnd - nav.startTime const load = nav.loadEventEnd - nav.startTime 工程建议结合资源级别数据与 Server-Timing 进行归因与路径治理。多会话聚合与设备网络分层分析，制定切实可行的优化计划。警惕跨源与隐私限制导致的字段缺失，进行兜底处理。参考与验证MDN：PerformanceNavigationTiming — https://developer.mozilla.org/docs/Web/API/PerformanceNavigationTimingW3C：Navigation Timing — https://www.w3.org/TR/navigation-timing-2/