Microsoft/vscode

[html] "Cannot redeclare block-scoped variable" in script type module

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#169,117 opened on Dec 14, 2022

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 (5 comments) (5 reactions) (1 assignee)TypeScript (74,848 stars) (10,221 forks)batch import
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Description

Does this issue occur when all extensions are disabled?: Yes

System:

  • VS Code Version: Version: 1.74.0
  • OS Version: macOS 13.0.1

Steps to Reproduce:

  1. Create a new HTML file
  2. Add two <script type="module"> and declare a variable with the same name in both (see example code below).
  3. Observe the red squiggly line underneath the variable names saying Cannot redeclare block-scoped variable.
image

When a script tag has the type attribute set to "module", the source text should be treated as an ES module with it's own scope, not the global scope.

https://developer.mozilla.org/en-US/docs/Web/HTML/Element/script#attr-type https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules#other_differences_between_modules_and_standard_scripts

Example HTML

<!DOCTYPE html>
<script type="module">
  const x = 1;
</script>
<script type="module">
  const x = 2;
</script>

Contributor guide

Tech stack
htmljavascripttypescript
Domain
developer experiencefrontend
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
blocked
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
JavaScript module scopingVS Code HTML language service
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
25
Research direction
Examine the VS Code HTML language service source code, particularly how script elements with type='module' are parsed and assigned scopes. Focus on files under 'extensions/html language features/server/src/'. The issue indicates that separate module scripts are incorrectly treated as sharing the same scope, causing 'Cannot redeclare block scoped variable' errors. The fix should ensure each module script has its own scope. Check the assignee's progress and any linked comments for more context.