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refactor(legacy): remove unneeded dynamic import var init code #7759



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@sapphi-red sapphi-red commented Apr 16, 2022


Currently plugin-legacy outputs html like below. (extracted the relevant part)

    <script type="module">var __vite_is_dynamic_import_support=false;</script>
    <script type="module">try{import("_").catch(()=>1);}catch(e){}window.__vite_is_dynamic_import_support=true;</script>
    <script type="module">!function(){if(window.__vite_is_dynamic_import_support)return;console.warn("vite: loading legacy build because dynamic import is unsupported, syntax error above should be ignored");var e=document.getElementById("vite-legacy-polyfill"),n=document.createElement("script");n.src=e.src,n.onload=function(){System.import(document.getElementById('vite-legacy-entry').getAttribute('data-src'))},document.body.appendChild(n)}();</script>

The first script tag is unused.
The reason is that a top level variable inside type="module" is not exposed to global.
It could be fixed by removing type="module" or changing to window.__vite_is_dynamic_import_support = false.
But since it is a falsy value, the declaration is not needed.
So I dropped this script tag.

This will simply the code a bit and also reduce file size of html (and csp header) a bit.

I tested this with in Chrome 102, Chrome 62, Edge 18, Firefox 66, Safari 10.1.

refs #6535

Additional context

What is the purpose of this pull request?

  • Bug fix
  • New Feature
  • Documentation update
  • Other

Before submitting the PR, please make sure you do the following

  • Read the Contributing Guidelines.
  • Read the Pull Request Guidelines and follow the Commit Convention.
  • Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
  • Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
  • Ideally, include relevant tests that fail without this PR but pass with it.

@sapphi-red sapphi-red added plugin: legacy p1-chore 🧹 Doesn't change code behavior (priority) labels Apr 16, 2022
@patak-dev patak-dev changed the title refactor(legacy): remove dynamic import var init code refactor(legacy): remove unneeded dynamic import var init code Apr 16, 2022
@patak-dev patak-dev merged commit 12a4e7d into vitejs:main Apr 16, 2022
@sapphi-red sapphi-red deleted the refactor/legacy-dynamic-import-support branch April 18, 2022 16:59
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p1-chore 🧹 Doesn't change code behavior (priority) plugin: legacy
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2 participants