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Stop using deprecated downlevelIteration#92652

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Apr 14, 2026
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Stop using deprecated downlevelIteration#92652
eps1lon merged 1 commit intocanaryfrom
sebbie/ts6-deprecation-downlevel-iteration

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@eps1lon eps1lon commented Apr 11, 2026

TypeScript transpiled ES6 iterators with downLevelIteration which was still used by @next/codemod and @next/refresh-utils. Currently supported Node.js versions and targets of Next.js support ES6 iterators so we should be able to safely get rid of downLevelIteration.

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eps1lon commented Apr 11, 2026

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Stats from current PR

✅ No significant changes detected

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  • Listen = TCP port starts accepting connections
  • First Request = HTTP server returns successful response
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Build Metrics:

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Change Thresholds:

  • Time: Changes < 50ms AND < 10%, OR < 2% are insignificant
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  • All other changes are flagged to catch regressions

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Metric Canary PR Change Trend
Cold (Listen) 455ms 456ms ▁▁▁▁▁
Cold (Ready in log) 439ms 439ms ▅▃▄▁▂
Cold (First Request) 821ms 820ms ▁█▁██
Warm (Listen) 455ms 456ms ▁▁▁▁▁
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Warm (First Request) 337ms 335ms ▂▆▄▅▆
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📦 Dev Server (Webpack)

Metric Canary PR Change Trend
Cold (Listen) 456ms 456ms ▅▁▅▅▅
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Cold (First Request) 1.895s 1.890s █▁▄▃▁
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Warm (Ready in log) 438ms 439ms █▂▁▁▂
Warm (First Request) 1.888s 1.886s █▁▃▂▂

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Metric Canary PR Change Trend
Fresh Build 3.956s 3.979s ▄▄▆▃▃
Cached Build 3.948s 3.946s ▆▁█▂▁
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📎 Tarball URL
https://vercel-packages.vercel.app/next/commits/a642e665e0928b08cd2e67ca023491ac653f0512/next

@eps1lon eps1lon changed the base branch from sebbie/ts6-rc-baseline to graphite-base/92652 April 12, 2026 09:31
@eps1lon eps1lon changed the title Remove deprecated downlevelIteration Stop using deprecated downlevelIteration Apr 14, 2026
@eps1lon eps1lon force-pushed the graphite-base/92652 branch from adfdf40 to fff4a4d Compare April 14, 2026 17:10
@eps1lon eps1lon force-pushed the sebbie/ts6-deprecation-downlevel-iteration branch from 325ba53 to a642e66 Compare April 14, 2026 17:10
@eps1lon eps1lon changed the base branch from graphite-base/92652 to canary April 14, 2026 17:10
@eps1lon eps1lon marked this pull request as ready for review April 14, 2026 17:32
@eps1lon eps1lon requested review from mischnic April 14, 2026 17:32
@eps1lon eps1lon merged commit 50847af into canary Apr 14, 2026
236 of 246 checks passed
@eps1lon eps1lon deleted the sebbie/ts6-deprecation-downlevel-iteration branch April 14, 2026 17:34
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