Web Storage

Web Storage works under Nub without a flag to remember. Node hides sessionStorage and localStorage behind --experimental-webstorage on the 22.4–24 band (native from 25), so Nub injects that flag for you on exactly that band — you never pass it. Below Node 22.4 the flag does not exist and Web Storage is unavailable.

Session storage

The sessionStorage global is in-memory and per-process: it is created fresh each run and discarded when the process exits, never touching disk. It works out of the box on Node 22.4+ — nothing to pass:

sessionStorage.setItem("step", "1");
sessionStorage.getItem("step");      // "1"
sessionStorage.length;               // 1
sessionStorage.key(0);               // "step"
sessionStorage.removeItem("step");
sessionStorage.clear();

A short walkthrough of a multi-step flow within one run:

sessionStorage.setItem("cursor", "0");

for (const page of pages) {
  const seen = Number(sessionStorage.getItem("cursor"));
  process(page, seen);
  sessionStorage.setItem("cursor", String(seen + 1));
}

console.log(sessionStorage.getItem("cursor")); // pages.length

Captured from Nub on Node 22.15.0 (no flag, no file passed):

$ nub session.ts
1
length 1

Local storage

The localStorage global persists across runs, so it needs a file on disk to write to. Pass --localstorage-file <path> and Nub forwards it to Node verbatim. Until you do, localStorage is undefined, so typeof localStorage === "undefined" is a feature check. Name a backing file and the global comes alive:

localStorage.setItem("token", "abc123");
localStorage.getItem("token");        // "abc123"
localStorage.length;                  // 1
localStorage.key(0);                  // "token"
localStorage.removeItem("token");
localStorage.clear();

Name the backing file and values survive between runs:

$ nub --localstorage-file=./app.db write.ts
abc123
$ nub --localstorage-file=./app.db read.ts
abc123

The --localstorage-file flag is also honored when set in NODE_OPTIONS.