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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

Abort outdated requests

A town guide offers rapid neighborhood lookups. The preview is intentionally powered by an explicit in-page mock fetch, so it works offline and never claims to show live data.

Imagine a slow neighborhood lookup followed quickly by a fast one. Without protection, the slow response may arrive last and overwrite the newer choice. AbortController provides a signal for a request; calling abort() tells fetch to reject it with an AbortError. A mock that accepts the same { signal } option lets us demonstrate that behavior offline.

javascript
let controller;
async function showDistrict(name) {
  controller?.abort();
  controller = new AbortController();
  try {
    const response = await mockFetch(`/api/district?q=${encodeURIComponent(name)}`, {
      signal: controller.signal
    });
    const district = await response.json();
    document.querySelector("#district").textContent = district.name;
  } catch (error) {
    if (error.name !== "AbortError") throw error;
  }
}

Click Slow: North then quickly Fast: South. The southern name remains even after the slow lookup would have finished. This fixture uses timers to mimic request latency, not network access. Inspect the controller in script.js: aborting previous work matters when a request is pending; an abort is an expected change of mind and should not be shown as a user-facing failure.

In a real network request, use fetch(url, { signal: controller.signal }). Some work after fetch may still continue independently, so complex multi-step operations can also check a request ID before painting the DOM. The exercise practices cancellation in a smaller view.

Learn more

MDN's AbortController shows its signal and cancellation methods.

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