Available since v0.1.0

fs-assert-mpa

Stable

Multi-page assertion. Marks an assertion to be persisted to localStorage on the current page and resolved on the next page load. Use for flows that straddle a hard navigation — form POSTs that redirect, legacy flows inside an SPA, anywhere a real pagehide + new DOMContentLoaded happens.

Syntax

fs-assert-mpa="true"

When to use it

A form submit triggers a real page reload and the success message appears on the next page
A legacy flow inside an otherwise-SPA app does a hard navigation
An auth handoff between origins (where the new origin has the agent installed)

For SPA-style client-side navigation (React Router, Vue Router, Turbo Drive), you do NOT need MPA mode — the agent session is long-lived across client-side route changes. A regular DOM assertion will wait for the new view to render and resolve naturally.

Example

<button
  fs-assert="mpa-form/submit"
  fs-trigger="click"
  fs-assert-mpa="true"
  fs-assert-visible=".success-message">
  Submit
</button>

On click, the assertion is serialized to localStorage. After the page reload, the agent reads it back and resolves it against the new page's DOM.

How it works

On trigger fire: the assertion is created normally AND written to localStorage with its current pending state.
On pagehide: the agent's unload handler flushes pending assertions (see timeout). MPA-marked assertions are left in storage, not failed.
On the next DOMContentLoaded: the agent reads stored MPA assertions and re-creates them in the new page's assertion manager.
Resolution: resolves against the new page's DOM via the normal paths — mutation observer for added / removed / updated, query for visible / hidden.

Pairs well with

fs-assert-visible — verify a success message rendered on the next page
fs-assert-added — verify a lazy-loaded element appears
fs-trigger="click" — form submissions that redirect
fs-trigger="submit" — same

Gotchas

Not compatible with emitted. MPA assertions persist to localStorage and resolve on the next page load — where the event will never re-fire. The agent warns and ignores fs-assert-mpa="true" on emitted assertions.
Not compatible with invariant. Invariants are perpetual for a single page lifetime.
Not compatible with hx-boost. hx-boost never fires a real unload, so MPA assertions under boost are written to storage but never reloaded — they orphan. Under hx-boost, the agent session is long-lived, so you don't need MPA: a regular DOM assertion resolves naturally across the virtual nav.
localStorage quota. MPA assertions are tiny but they share the same quota as your app. Clean up is automatic on resolution or timeout.
Cross-origin navigation. MPA survives a same-origin redirect. It does not survive navigation to a different origin — localStorage is origin-scoped.