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← DOM Manipulation with JavaScript
○The page is a tree○Exercise: follow the document reference○Load a script when the page is ready○Exercise: initialize a deferred script○Find one element by id or CSS selector○Exercise: select a notice and label○Compare DOM properties, HTML attributes, and node types○Exercise: inspect a room input and its nodes✦Module Quiz
○Find every match with querySelectorAll○Exercise: label every trail stop○Move from a child to its relatives○Exercise: trace a nested card○Check for missing elements and search within a card○Exercise: update only the chosen card○Compare a live HTMLCollection with a static NodeList○Exercise: safely expand a live collection✦Module Quiz
○Safe text and HTML○Exercise: render a safe notice○Read and change link attributes○Exercise: update an accessible link○Data attributes and conditional text○Exercise: announce session availability○Boolean attributes and DOM properties○Exercise: unlock a volunteer sign-up✦Module Quiz
○Add, remove, and check classes○Exercise: mark a favourite card○Toggle a panel accessibly○Exercise: toggle the help panel○Inline styles, classes, and hidden○Exercise: style and hide a notice○Change a CSS custom property from JavaScript○Exercise: change a workshop card accent✦Module Quiz
○Create and Append a Text Node○Exercise: Add a Reading List Item○Place Nodes Before and Between○Exercise: Order the Workshop Agenda○Remove, Replace, and Clear Safely○Exercise: Refresh a Museum Display○Clone a Card and Insert a Batch○Exercise: Clone Two Exhibit Cards✦Module Quiz
○Listen for Clicks with a Named Handler○Exercise: Check Library Hours○Event Target, Current Target, and Delegation○Exercise: Delegate Pantry Actions○Keyboard Events Without Trapping Keys○Exercise: Search the Recipe Box○Once, Remove, and Bubble○Exercise: Control Workshop Notifications✦Module Quiz
○Read a field while someone types○Build a live name preview○Handle submit without leaving the page○Validate a library request○Keep a selection in sync on change and reset○Sync a preference and its reset state○Read multiple checked values with FormData○Build a checkbox-based garden request✦Module Quiz
○Filter a list as someone types○Build a live trail finder○Toggle an accessible disclosure○Build a guide menu disclosure○Create and remove items with one delegated listener○Build a neighborhood task board○Sort a workshop table with accessible buttons○Build an accessible sortable resource table✦Module Quiz
○Read selectable cards and detail updates○Build directory cards and a selected profile○Trace live search and an empty state○Add live search to the community directory○Trace safe additions and delegated removal○Add and remove community directory cards✦Module Quiz
○Read and update a live itinerary○Build the workshop itinerary○Add a validated item through a form○Add a workshop session○Filter and remove live entries○Finish the workshop planner✦Module Quiz
○Fetch JSON and render safe text○Exercise: load recipe cards○Handle loading, empty, and failed responses○Exercise: handle alert states○Build a query with URLSearchParams○Exercise: search the catalog○Abort outdated requests●Exercise: keep the latest result✦Module Quiz
○Load a dashboard from an offline API fixture○Build an events dashboard○Query a dashboard with URLSearchParams○Add event search to the dashboard○Retry requests without stale results○Finish a resilient event dashboard✦Module Quiz

Exercise: keep the latest result

A ferry board has two routes; only the most recent selection should win. The preview is intentionally powered by an explicit in-page mock fetch, so it works offline and never claims to show live data.

The previous district lookup canceled a slow old request. Now a ferry board must do the same for two route buttons. The supplied mockFetch(url, { signal }) records a local request, waits for a predictable timer, and rejects with AbortError if canceled. It never contacts a ferry service.

For an unrelated temperature display the pattern is:

javascript
let currentController;
async function checkWeather(city) {
  currentController?.abort();
  currentController = new AbortController();
  try {
    const response = await mockFetch(`/api/weather?city=${encodeURIComponent(city)}`, {
      signal: currentController.signal
    });
    const data = await response.json();
    label.textContent = data.summary;
  } catch (error) {
    if (error.name !== "AbortError") label.textContent = "Lookup failed.";
  }
}

In the ferry board, click Slow pier and immediately Fast pier. The board should end on Fast even when the slow timer has elapsed. AbortError is not a service outage; don't replace the newer loading or ready message with an error from the canceled request. Run the preview, then Submit for checks that exercise both cancellation and the final DOM state.

Your Task

  1. Wire both route buttons to start mockFetch for their route and immediately announce Loading route….
  2. On a newer click, abort the previous request with AbortController and pass each request its controller’s signal.
  3. Render only the latest route name as literal text and report Route ready. after its response arrives.
  4. Ignore an old request’s AbortError so it never replaces the newest route’s ready status with an error.
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