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Table of Contents
如何開(kāi)始一次性能記錄
怎么看關(guān)鍵指標(biāo)和瓶頸
常見(jiàn)問(wèn)題定位方法
幾個(gè)實(shí)用小技巧
Home Web Front-end Front-end Q&A How to use browser developer tools performance tab

How to use browser developer tools performance tab

Jul 02, 2025 am 12:14 AM

打開(kāi) Performance 面板可直接查看頁(yè)面加載過(guò)程中的性能問(wèn)題,是優(yōu)化頁(yè)面性能的關(guān)鍵手段。1. 開(kāi)始記錄:點(diǎn)擊錄制按鈕或快捷鍵 Ctrl+E,進(jìn)行操作后停止錄制,即可看到包含腳本、渲染、網(wǎng)絡(luò)請(qǐng)求等事件的時(shí)間軸;2. 查看關(guān)鍵指標(biāo):關(guān)注 FCP、LCP 和 TTI 等核心指標(biāo),判斷頁(yè)面加載速度與交互準(zhǔn)備時(shí)間;3. 定位瓶頸:通過(guò)長(zhǎng)任務(wù)、強(qiáng)制同步布局、資源過(guò)大、頻繁 layout/paint 操作等線索識(shí)別性能問(wèn)題;4. 使用火焰圖、放大時(shí)間段、對(duì)比不同版本等技巧輔助分析。掌握這些步驟能有效提升性能排查效率。

打開(kāi)瀏覽器開(kāi)發(fā)者工具的 Performance 標(biāo)簽,其實(shí)是做頁(yè)面性能優(yōu)化最直接也最有用的方式之一。它能告訴你頁(yè)面加載過(guò)程中都發(fā)生了什么,哪里卡了、哪里慢了、資源怎么分布的。

下面幾個(gè)部分,是使用 Performance 面板時(shí)你最可能關(guān)心的事,也是實(shí)際工作中排查性能問(wèn)題的關(guān)鍵點(diǎn)。


如何開(kāi)始一次性能記錄

Performance 標(biāo)簽的核心功能是“錄制”頁(yè)面在一段時(shí)間內(nèi)的行為。操作很簡(jiǎn)單:

  • 打開(kāi) DevTools(F12 或右鍵檢查)
  • 切換到 Performance 標(biāo)簽
  • 點(diǎn)擊左上角的圓形“錄制”按鈕(或快捷鍵 Ctrl+E)
  • 進(jìn)行你要分析的操作(比如刷新頁(yè)面、點(diǎn)擊某個(gè)按鈕)
  • 再次點(diǎn)擊停止錄制

這時(shí)候你會(huì)看到一個(gè)時(shí)間軸,里面包含了加載過(guò)程中的各種事件:腳本執(zhí)行、渲染、網(wǎng)絡(luò)請(qǐng)求等。

小技巧:如果你只想看頁(yè)面首次加載的表現(xiàn),可以勾選“Disable cache”再刷新頁(yè)面,這樣模擬的是用戶第一次訪問(wèn)的情況。


怎么看關(guān)鍵指標(biāo)和瓶頸

記錄完成后,Performance 會(huì)展示一張?jiān)敿?xì)的時(shí)間線圖。你可以從以下幾個(gè)方面入手:

  • FCP(First Contentful Paint):第一個(gè)內(nèi)容繪制時(shí)間,表示頁(yè)面開(kāi)始有東西出現(xiàn)的時(shí)間點(diǎn)。
  • LCP(Largest Contentful Paint):最大內(nèi)容繪制時(shí)間,通常影響用戶感知加載速度。
  • TTI(Time to Interactive):頁(yè)面變得完全可交互的時(shí)間,也就是主線程空閑下來(lái)的時(shí)候。

這些指標(biāo)都會(huì)以橙色或藍(lán)色的小標(biāo)記顯示在圖表頂部。你可以通過(guò)它們大致判斷頁(yè)面是否“夠快”。

如果你發(fā)現(xiàn)某段時(shí)間主線程被大量 JS 占據(jù),那可能是腳本執(zhí)行太重了;如果網(wǎng)絡(luò)請(qǐng)求很多且耗時(shí)長(zhǎng),那可能是資源太大或者請(qǐng)求數(shù)太多。


常見(jiàn)問(wèn)題定位方法

Performance 圖表中有一些明顯的線索可以幫助你發(fā)現(xiàn)問(wèn)題:

  • 長(zhǎng)任務(wù)(Long Tasks):紅色條塊表示主線程阻塞超過(guò)50ms的任務(wù),這可能導(dǎo)致頁(yè)面卡頓。
  • 頻繁的強(qiáng)制同步布局(Forced Synchronous Layout):如果有黃色警告提示,說(shuō)明代碼中有觸發(fā)回流的設(shè)計(jì)問(wèn)題。
  • 過(guò)大的 JS/CSS 文件:查看 Network 區(qū)域,看看主資源是否過(guò)大,有沒(méi)有壓縮空間。
  • 過(guò)多的 layout/paint 操作:頻繁的渲染動(dòng)作可能意味著 DOM 操作不當(dāng)或動(dòng)畫(huà)設(shè)計(jì)不合理。

建議每次分析完記錄后,先從主線程活動(dòng)入手,再結(jié)合網(wǎng)絡(luò)面板看看資源加載情況。


幾個(gè)實(shí)用小技巧

  • 使用火焰圖快速識(shí)別熱點(diǎn):火焰圖中每一層代表一個(gè)函數(shù)調(diào)用棧,越寬表示耗時(shí)越久??梢杂脕?lái)找出執(zhí)行時(shí)間最長(zhǎng)的函數(shù)。
  • 放大特定時(shí)間段觀察細(xì)節(jié):鼠標(biāo)拖動(dòng)上方時(shí)間軸可以聚焦到某一秒內(nèi),方便深入分析。
  • 對(duì)比不同版本的表現(xiàn)差異:比如改了一個(gè)組件之后,錄兩次 Performance,對(duì)比兩個(gè)結(jié)果,更容易看出改動(dòng)是否有性能收益。

基本上就這些。別被一堆圖表嚇住,一開(kāi)始只需要關(guān)注主線程和幾個(gè)核心指標(biāo)就夠了。慢慢你會(huì)發(fā)現(xiàn),這個(gè)面板其實(shí)挺直觀的,而且信息量非常大。

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