parcel-bundler/parcel

Module scripts loaded with low priority when compiled

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#6,981 建立於 2021年9月23日

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:bug: BugGood First Issue✨ Parcel 2

描述

Native module scripts (e.g. <script type="module">) are typically loaded by browsers with high priority. However, when targeting browsers without native support, Parcel inserts <script defer nomodule> tags, which are loaded with low priority. See https://addyosmani.com/blog/script-priorities/.

With that said, these scripts still need the defer attribute to emulate the execution timing of native modules. One workaround to boost priority of deferred scripts is to also insert a <link rel="preload" as="script"> into the document head with an href with the same value as the script's src.

We should consider adding these link tags as well when including js targeted at these environments.

Related: #6980

貢獻者指南

技術棧
javascripthtmlcss
領域
frontendperformance
議題類型
feature
難度面向新貢獻者的預計實作難度，1 表示很小改動，5 表示專家級工作。
3
預計時間有經驗貢獻者完成調查、實作、測試並準備 pull request 的粗略時間範圍。
half day
活動狀態議題目前的可參與程度：新鮮、活躍、陳舊、阻塞或等待維護者輸入。
fresh
清晰度議題是否清楚說明預期改動、驗收標準和下一步。
mostly clear
前置要求
Basic understanding of Parcel bundlerKnowledge of script loading priorities
新手友善度1-100 的估計分數，表示該議題對首次貢獻者的友善程度。
55
研究方向
Investigate how Parcel currently generates `<script defer nomodule>` tags for non module targets. Look at the bundler's HTML asset handling, likely in packages/core/integration tests or similar. Consider adding logic to insert `<link rel="preload" as="script">` for each deferred script. Related issue #6980 provides additional context.