Deno v1.21.0 — Release Notes & Engineering Impact

Source available — automated, not human-reviewed

Component: deno · Channel: stable. Automated analysis, not a compatibility certification. How this works.

Analysis updated: 2026-11-01.

Compatibility not verified — check source notes

📄 .MD

✨ Features 6 ⚡ Improvements 3 🔧 Bug Fixes 6

⚡ Executive Summary (TL;DR)

Deno v1.21.0. Source highlight: View the full release blog post here.

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Who Does This Impact? (Role-Based Analysis)

💻 Software Engineers & Devs

Check the source notes against the package and APIs you use before upgrading.

📊 Product & Engineering Leads

Use the documented changes to assess relevance to your product; release frequency alone is not a quality measure.

⚙️ DevOps & Security

Verify the target version, runtime requirements and rollback procedure in the official documentation.

✨ New Features & Capabilities (6)

feat(bench): update API, new console reporter (#14305)
feat(cli/fmt): ignore .git folder when formatting files (#14138)
feat(core): Add initial support for realms (#14019)
feat(ext/net): `Deno.upgradeHttp` handles unix connections (#13987)
feat(ext/web): add globalThis.reportError() (#13799)
feat(repl): Don't type check when importing modules (#14112)

⚡ Performance & Enhancements (3)

perf(fmt/lint): incremental formatting and linting (#14314)
perf(runtime): bypass tokio file and bump op buffer size to 64K (#14319)
perf: move `Deno.writeTextFile` and like functions to Rust (#14221)

🔧 Bug Fixes & Patches (6)

fix(cli/emit): Check JS roots with `// @ts-check` (#14090)
fix(cli/tools/test): Prefix test module paths with `./` (#14301)
fix(fmt): regression where some short if stmt headers being split on multiple
fix(permissions): fallback to denied access if the permission prompt fails
fix: `--watch` was losing items (#14317)
fix: panic when trying to pledge permissions before restoring previous pledge

📄 View Raw Release Notes (Original Developer Log)

View the full release blog post [here](https://deno.com/blog/v1.21). ### 1.21.0 / 2022.04.20 - feat(bench): update API, new console reporter (#14305) - feat(cli/fmt): ignore .git folder when formatting files (#14138) - feat(core): Add initial support for realms (#14019) - feat(ext/net): `Deno.upgradeHttp` handles unix connections (#13987) - feat(ext/web): add globalThis.reportError() (#13799) - feat(repl): Don't type check when importing modules (#14112) - feat(repl): add `--eval-file` flag to execute a script file on startup (#14247) - feat(repl): add global `clear()` function (#14332) - feat(runtime): two-tier subprocess API (#11618) - feat(test): Add `name`, `origin` and `parent` to `Deno.TestContext` (#14007) - feat(test): Improve testing report output (#14255) - feat(test): format user code output (#14271) - feat(test): skip internal stack frames for errors (#14302) - feat(test): use structured data for JavaScript errors in tests (#14287) - feat: Add "deno check" subcommand for type checking (#14072) - feat: Add `DENO_NO_PROMPT` variable (#14209) - feat: Better formatting for `AggregateError` (#14285) - fix(cli/emit): Check JS roots with `// @ts-check` (#14090) - fix(cli/tools/test): Prefix test module paths with `./` (#14301) - fix(fmt): regression where some short if stmt headers being split on multiple lines (#14292) - fix(permissions): fallback to denied access if the permission prompt fails (#14235) - fix: `--watch` was losing items (#14317) - fix: panic when trying to pledge permissions before restoring previous pledge (#14306) - perf(fmt/lint): incremental formatting and linting (#14314) - perf(runtime): bypass tokio file and bump op buffer size to 64K (#14319) - perf: move `Deno.writeTextFile` and like functions to Rust (#14221) - upgrade: rusty_v8 0.42.0 (#14334)

← Older Version Deno v1.20.6 Newer Version → Deno v1.21.1