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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: safely expand a live collection

At the pond, a live HTMLCollection gained a new sighting while a NodeList captured earlier stayed the same size. Now a makerspace has two station cards. Each existing station needs a — staffed label and a matching — backup station. The new backup stations must not be processed during this pass.

A separate pattern for a gallery would freeze its current paintings before adding anything:

javascript
const livePaintings = document.getElementsByClassName("painting");
const firstPaintings = document.querySelectorAll(".painting");
const snapshot = Array.from(livePaintings);
snapshot.forEach((painting) => {
  // Process only paintings that existed when snapshot was made.
});

The starter already takes the live collection, the earlier static NodeList, and a fixed originalStations snapshot. Work from that snapshot, not from the changing live collection: appending matching nodes while iterating a live collection can keep extending the work. First label the originals ** — staffed**. Then add backups by removing that suffix from each original name (or by saving the names first). Make each backup with document.createElement("li"), set its className to "station" and textContent to the original name plus ** — backup**, then append it to #stations. These node-creation calls are the same ones you just saw in the pond demo; the later node-creation section will explore them in depth. Run: the live count is 4, static count 2, and backup rows do not say staffed.

Your Task

  1. Use originalStations to label the two original stations — staffed.
  2. Use originalStations to add exactly one li.station backup for each, named with the original station text plus — backup (without staffed).
  3. Show the final liveStations.length in #live-count after appending.
  4. Show the earlier initialStations.length in #static-count.
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