Pin HashHistory: one route stack per browser window

Welcome 👋

Neo apps route by the URL hash, and Neo can run one app across several browser windows. Neo.util.HashHistory remembers the recent routes: one stack per window, newest first. It is about sixty lines of plain logic with no test, which makes it a good first spec.

This is a good first issue for Hacktoberfest 2026. It needs Node.js and a clone of this repository: no Docker, no AI setup.

[!IMPORTANT] Reserved for first-time Neo.mjs contributors. The maintainer team will not claim, edit, or implement this issue through 2026-10-31. Comment here to claim it, and ask anything on this issue.

Set up once: follow Set up the engine from a clone, including npm run bundle-browser-deps: without it the unit suite selects zero tests.

Where things live

• Source: src/util/HashHistory.mjs, a singleton with push(data), first(), second(), getAt(), getCount(), getStack() and a change event
• New test file: test/playwright/unit/util/HashHistory.spec.mjs
• Pattern to copy: test/playwright/unit/util/Array.spec.mjs (the setup() call and imports)
• Tip: it is a singleton, so its stacks survive from one test to the next. Start each test with HashHistory.stacks = {}.

What to cover

Something to look at while you are in there: push() runs delete data[windowId]. That deletes a property named after the window id's value (for example data['w1']), not the windowId property itself. Pin what the code does today. If you think it meant delete data.windowId, say so on this issue before changing src/: that is a behaviour change, and #5492 introduced the line.

Done when

• test/playwright/unit/util/HashHistory.spec.mjs exists, following the pattern file's setup.
• One test(...) per table row.
• Test-only, as above.
• npm run test-unit -- test/playwright/unit/util/HashHistory.spec.mjs passes.
• npm run test-unit passes.

Out of scope

The router and controllers that read the history (src/controller/Base.mjs), and browser integration.

While you wait for review

You just pinned one small piece of a multi-threaded application engine: in Neo.mjs your app's code runs inside a web worker, and the main thread only paints. Two things worth ten minutes:

• See the part nobody expects. Run npm run build-themes -- -n -e dev -t all and npm run server-start, open apps/workstation/, and drag a tab out of the browser window. It becomes its own OS window, still running, with the same component instances and the same worker. Benefits: Introduction explains why that is possible.
• Your coding agent can go much further here. The skills this repository's AI maintainers work with are published on npm as neo-agent-skills, and they need no Knowledge Base and no Memory Core. With Claude or GPT beside you, the help wanted issues are within reach after this one.