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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

Handle loading, empty, and failed responses

A library desk must report both successful and unsuccessful lookups. The preview is intentionally powered by an explicit in-page mock fetch, so it works offline and never claims to show live data.

A library lookup can fail in two different ways. A server may respond with HTTP 503; fetch still resolves to a Response, so inspect response.ok before reading JSON. A disconnected network or CORS denial instead rejects the Promise and goes to catch. Both need a useful message rather than an unhandled error.

javascript
async function readRecord() {
  status.textContent = "Loading…";
  try {
    const response = await mockFetch("/api/record");
    if (!response.ok) throw new Error(`HTTP ${response.status}`);
    const data = await response.json();
    status.textContent = data.length ? "Ready." : "No records found.";
  } catch (error) {
    status.textContent = `Could not load: ${error.message}`;
  }
}

The preview uses four selectable offline mock scenarios: records, empty array, HTTP failure, and a simulated network rejection. It does not report live service availability. Run each selection. Loading appears before the Promise settles; empty is a successful result, not an error. The catch message avoids pretending an HTTP response existed when the network never delivered one.

Notice that JSON parsing happens after the ok check. An error body need not have the same shape as a successful array. The next exercise asks you to give a different noticeboard these same four honest states.

Learn more

MDN's Response.ok documents the success-status check.

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