cannot redeclare block scoped variable postMessage()

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#55,752 4 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
32/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
typescript
Domain
compilers

Research direction

Start with the SharedWorker example and the separate tsconfig.json files in the NPM-workspaces monorepo. Inspect the duplicate postMessage declarations in lib.dom.d.ts and determine why they enter the same TypeScript program; verify the fix by rebuilding the affected modules and confirming the diagnostic is gone.

Written by the indexing model from the issue text.

Description

Needs More Info
🔎 Search Terms

"cannot redeclare block scope variable postMessage typescript"

🕗 Version & Regression Information

TS version: ^5.1.6

⏯ Playground Link

Can't use workers in Playground

💻 Code
const worker = new SharedWorker(new URL('./worker.js', import.meta.url))

/* ... */

worker.port.addEventListener('message', e => {
     if (!e.data?.type) {
          return
      }

      switch (e.data.type) {
          case 'get_tabs': {
               worker.port.postMessage({ //Error here
                   type: 'share_tab_id',
                   tab_id: tabId
               })
          }

    /* ... */
🙁 Actual behavior

I'm getting a Cannot redeclare block-scoped variable 'postMessage' error coming from TypeScript itself. I checked the file (lib.dom.d.ts) and it looks like the postMessage variable is getting declared twice

ts-postmessage-error
ts-postmessage-declaration

🙂 Expected behavior

Expect to have single declaration of postMessage and no error.

Additional information about the issue

I'm using a monorepo with NPM workspaces. Each module has a separate tsconfig.json and are built separately

Dominant language
Go
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Avg merge
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Merged PRs (30d)
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