摘要：搭建更新代碼的腳手架加載化使用基于的緩存機(jī)制，就需要一個腳手架來管理資源文件的讀取和寫入，不難看出微信使用的是自己開發(fā)的腳手架，閱讀其源碼代價較大，暫不分析。

事情的起因是我的同事金果問我：
- “你知道微信公眾號文章的渲染方式嗎？”

對此，我的反應(yīng)是：
- “啊？”

金果繼續(xù)問：
- “控制臺的 Network 里沒有發(fā)生任何請求，文章里的內(nèi)容是怎么來的？”

說到這兒我好像大概理解她的意思，于是打開控制臺的 Network 確認(rèn)一下果真如此，文章中的內(nèi)容并不是通過 http 請求獲取的。

首先我想到的是：
- “會不會是服務(wù)器端渲染的？”

于是我找到請求得到的 html 文件卻發(fā)現(xiàn)：

- “只有文章的標(biāo)題是服務(wù)器端渲染的，那么文章的內(nèi)容就只能在 js 文件中。”

我繼續(xù)尋找請求得到的 js 文件卻發(fā)現(xiàn)空空如也：
- “難道 js 文件都被緩存到 localStorage 里？！”

看到 Local Storage 里密密麻麻的 js 文件我心里一陣澎湃：這確實是一種可以嘗試的前端加載性能優(yōu)化的方式。

項目在迭代開發(fā)的過程中，難以避免需要更新資源文件，常用的方法有`文件名${md5}.js`或者在資源 url 后面加上特定后綴的方式 etc.，而在微信做法中以 __MOON__pages/report.js 為例，其版本信息使用 key 為 __MOON__pages/report.js_ver 的存儲項保存：

__MOON__pages/report.js_ver: //res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/pages/report3b8dd6.js

我們不直接使用這個 value 動態(tài)插入 script 節(jié)點來加載該文件，而是根據(jù)后端提供的配置信息，判斷是選擇使用緩存的 __MOON__pages/report.js 文件，還是重新發(fā)起加載請求。

（加載 combo 化）使用基于 localStorage 的緩存機(jī)制，就需要一個腳手架來管理資源文件的讀取和寫入，不難看出微信使用的是自己開發(fā)的腳手架 moon.js，閱讀其源碼代價較大，暫不分析。

前端在進(jìn)行資源更新時需要后端提供一份依據(jù)供前端用于判斷哪些資源需要更新，并且腳手架 moon.js 需要該資源配置信息才能正常工作，所以配置信息一定要在 moon.js 的 script 標(biāo)簽前輸出：

window.moon_map = 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s/http.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/biz_common/utils/http3518c6.js","biz_common/utils/cookie.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/biz_common/utils/cookie3518c6.js","appmsg/topic_tpl.html.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/topic_tpl.html31ff31.js","pages/weapp_tpl.html.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/pages/weapp_tpl.html36906d.js","biz_common/utils/monitor.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/biz_common/utils/monitor3518c6.js","appmsg/weapp_common.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/weapp_common3af55a.js","pages/voice_tpl.html.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/pages/voice_tpl.html38518d.js","pages/kugoumusic_ctrl.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/pages/kugoumusic_ctrl393e3a.js","pages/qqmusic_ctrl.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/pages/qqmusic_ctrl39b68c.js","pages/voice_component.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/pages/voice_component3af14e.js","pages/qqmusic_tpl.html.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/pages/qqmusic_tpl.html393e3a.js","new_video/ctl.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/new_video/ctl2d441f.js","a/testdata.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/a/testdata3b86a9.js","appmsg/reward_entry.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/reward_entry3b1cff.js","appmsg/comment.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/comment3944ad.js","appmsg/like.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/like375fea.js","pages/version4video.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/pages/version4video3a9bef.js","a/a.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/a/a3b8ecd.js","rt/appmsg/getappmsgext.rt.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/rt/appmsg/getappmsgext.rt2c21f6.js","biz_wap/utils/storage.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/biz_wap/utils/storage34c264.js","biz_common/tmpl.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/biz_common/tmpl3518c6.js","appmsg/share_tpl.html.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/share_tpl.html36906d.js","appmsg/img_copyright_tpl.html.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/img_copyright_tpl.html2a2c13.js","pages/video_ctrl.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/pages/video_ctrl36ebcf.js","biz_common/ui/imgonepx.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/biz_common/ui/imgonepx3518c6.js","biz_common/utils/respTypes.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/biz_common/utils/respTypes3518c6.js","biz_wap/utils/log.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/biz_wap/utils/log34c264.js","sougou/index.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/sougou/index36913b.js","biz_wap/safe/mutation_observer_report.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/biz_wap/safe/mutation_observer_report34c264.js","appmsg/fereport.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/fereport3b9457.js","appmsg/report.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/report3404b3.js","appmsg/report_and_source.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/report_and_source3a7477.js","appmsg/page_pos.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/page_pos3a95b8.js","appmsg/cdn_speed_report.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/cdn_speed_report3097b2.js","appmsg/wxtopic.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/wxtopic31a3be.js","appmsg/new_index.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/new_index36906d.js","appmsg/weapp.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/weapp3af55a.js","appmsg/weproduct.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/weproduct3af55a.js","appmsg/voicemsg.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/voicemsg3b1748.js","appmsg/autoread.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/autoread3af14e.js","appmsg/voice.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/voice38518d.js","appmsg/qqmusic.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/qqmusic39dc43.js","appmsg/iframe.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/iframe39ab71.js","appmsg/product.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/product393966.js","appmsg/review_image.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/review_image3af55a.js","appmsg/outer_link.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/outer_link275627.js","appmsg/copyright_report.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/copyright_report2ec4b2.js","appmsg/async.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/async3b27d5.js","biz_wap/ui/lazyload_img.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/biz_wap/ui/lazyload_img3af55a.js","biz_common/log/jserr.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/biz_common/log/jserr3518c6.js","appmsg/share.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/share3b4418.js","appmsg/cdn_img_lib.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/cdn_img_lib38b7bb.js","biz_common/utils/url/parse.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/biz_common/utils/url/parse36ebcf.js","page/appmsg/not_in_mm.css":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/style/page/appmsg/not_in_mm.css36906d.js","page/appmsg/page_mp_article_improve_combo.css":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/style/page/appmsg/page_mp_article_improve_combo.css3b86a9.js","page/appmsg_new/not_in_mm.css":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/style/page/appmsg_new/not_in_mm.css36f05c.js","page/appmsg_new/combo.css":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/style/page/appmsg_new/combo.css3b86a9.js","biz_wap/jsapi/core.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/biz_wap/jsapi/core3b0568.js","biz_common/dom/event.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/biz_common/dom/event3a25e9.js","appmsg/test.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/test354009.js","biz_wap/utils/mmversion.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/biz_wap/utils/mmversion34c264.js","appmsg/max_age.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/max_age2fdd28.js","biz_common/dom/attr.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/biz_common/dom/attr3518c6.js","biz_wap/utils/ajax.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/biz_wap/utils/ajax38c31a.js","appmsg/log.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/log300330.js","biz_common/dom/class.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/biz_common/dom/class3518c6.js","biz_wap/utils/device.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/biz_wap/utils/device34c264.js","biz_common/utils/string/html.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/biz_common/utils/string/html3518c6.js","appmsg/index.js":"http://res.wx.qq.com/mmbizwap/zh_CN/htmledition/js/appmsg/index3b1748.js"};

在 __MOON__pages/report.js 文件的入口處加入代碼 alert("Helo World"); 如圖所示：

刷新頁面后彈出提示 “Hello World”，說明使用基于 localStorage 的緩存機(jī)制存在一些安全隱患，并且微信尚未對這些攻擊漏洞進(jìn)行處理。

如果先輸出 html 然后用 js 從本地緩存讀取樣式再插入會出現(xiàn)嚴(yán)重的阻塞和閃爍問題

這種解決方案更加適合單頁面應(yīng)用否則容易產(chǎn)生冗余

存在瀏覽器兼容性問題（隱身模式 etc.）（微信具有自己的X5內(nèi)核完美解決該問題）

網(wǎng)絡(luò)速度快，協(xié)商緩存的響應(yīng)延遲可能比 LS讀取+eval 更小

瀏覽器對于單次 set 和對 LS（本質(zhì)是 SQL lite）的總?cè)萘看嬖谙拗?/p>

可以節(jié)省流量，并且可以用于 A/B test

移動端的瀏覽器緩存經(jīng)常會被清理且網(wǎng)絡(luò)狀態(tài)通常較差，更加適合這種解決方案

https://github.com/scrat-team...
https://github.com/mtjs/mt

最后突然想起一句話：不要指望代碼能解決一切問題。