⚠️ Breaking Change
Impact Score: 7/10
Deno v0.40.0 — 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.
Breaking-change evidence from the source
- BREAKING: Rename 'deno fetch' subcommand to 'deno cache' (#4656)
- BREAKING: Remove std/testing/runner.ts (#4649)
⚡ Executive Summary (TL;DR)
Deno v0.40.0. Source highlight: BREAKING: Rename 'deno fetch' subcommand to 'deno cache' (#4656)
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.
⚠️ Breaking Changes & Deprecations (2)
- - BREAKING: Rename 'deno fetch' subcommand to 'deno cache' (#4656)
- - BREAKING: Remove std/testing/runner.ts (#4649)
✨ New Features & Capabilities (6)
- feat(std/flags): Pass key and value to unknown (#4637)
- feat(std/http): Respond with 400 on request parse failure (#4614)
- feat(std/node): Add exists and existsSync (#4655)
- feat: Add File support in FormData (#4632)
- feat: Expose ReadableStream and make Blob more standardized (#4581)
- feat: add --importmap flag to deno bundle (#4651)
🔧 Bug Fixes & Patches (6)
- fix(#4546): Added Math.trunc to toSecondsFromEpoch to conform the result to u64 (#4575)
- fix(file_server): use text/typescript instead of application/typescript (#4620)
- fix(std/testing): format bigint (#4626)
- fix: Drop headers with trailing whitespace in header name (#4642)
- fix: Fetch reference types for JS files (#4652)
- fix: Improve deno doc (#4672, #4625)
📄 View Raw Release Notes (Original Developer Log)
### Changes
- BREAKING: Rename 'deno fetch' subcommand to 'deno cache' (#4656)
- BREAKING: Remove std/testing/runner.ts (#4649)
- feat(std/flags): Pass key and value to unknown (#4637)
- feat(std/http): Respond with 400 on request parse failure (#4614)
- feat(std/node): Add exists and existsSync (#4655)
- feat: Add File support in FormData (#4632)
- feat: Expose ReadableStream and make Blob more standardized (#4581)
- feat: add --importmap flag to deno bundle (#4651)
- fix(#4546): Added Math.trunc to toSecondsFromEpoch to conform the result to u64 (#4575)
- fix(file_server): use text/typescript instead of application/typescript (#4620)
- fix(std/testing): format bigint (#4626)
- fix: Drop headers with trailing whitespace in header name (#4642)
- fix: Fetch reference types for JS files (#4652)
- fix: Improve deno doc (#4672, #4625)
- fix: On init create disk_cache directory if it doesn't already exists (#4617)
- fix: Remove unnecessary namespaces in "deno types" (#4677, #4675, #4669, #4668, #4665, #4663, #4662)
- upgrade: Rust crates (#4679)
### Install / Upgrade
**Using Deno:**
```sh
deno upgrade
```
**With Shell:**
```sh
curl -fsSL https://deno.land/x/install/install.sh | sh -s v0.40.0
```
**With PowerShell:**
```powershell
iwr https://deno.land/x/install/install.ps1 -useb -outf install.ps1; .\install.ps1 v0.40.0
```