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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: handle alert states

A trail-alert board must say whether there are alerts or a request failed. 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 library demo separated three outcomes: a nonempty array, an empty array, and a failed request. Here the selectable alert fixture also supports HTTP 503 and a rejected Promise. The values are deterministic local examples, not the current conditions on any trail.

An unrelated shipping-status viewer could start like this:

javascript
async function checkShipment() {
  message.textContent = "Checking…";
  try {
    const response = await mockFetch("/api/shipment");
    if (!response.ok) throw new Error(`HTTP ${response.status}`);
    const events = await response.json();
    message.textContent = events.length ? "Events found." : "No events yet.";
  } catch (error) {
    message.textContent = `Unable to check: ${error.message}`;
  }
}

For the alert board, choose a scenario and click Check alerts. Read the status before and after the asynchronous result. Build alert items with textContent; use the status to distinguish “no alerts” from “could not check.” response.ok is required even though the mock returns a Response, because a Response with 503 is still delivered successfully to JavaScript.

Your Task

  1. On click, immediately show Checking alerts… and start mockFetch for the selected mode.
  2. For a successful nonempty response, await JSON and render each title as text-only li elements.
  3. For a successful empty response, clear earlier alerts and say No alerts right now..
  4. Check response.ok before JSON; on an HTTP failure clear old alerts and say Could not load alerts..
  5. Handle a rejected network request with the same cleared list and error status.
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