性能监控问题

function testPerformance(){
　　let performance = window.performance
　　let timing = performance.timing
　　console.log('白屏时间',timing.responseEnd - timing.navigationStart)
　　console.log('页面总下载时间.',timing.loadEventEnd - timing.navigationStart)
　　console.log('DNS解析耗时.',timing.domainLookupEnd - timing.domainLookupStart)
　　console.log('TCP链接耗时.',timing.connectEnd - timing.connectStart)
　　console.log('首包请求耗时.',timing.responseEnd - timing.responseStart)
　　console.log('dom解释耗时.',timing.domComplete - timing.domInteractive)
　　console.log('用户可操作时间.',timing.domContentLoadedEventEnd - timing.navigationStart)
}