• do
InterCourses
CoursesBlogs
0
← 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

Add, remove, and check classes

A programme card needs a quick highlight control. Instead of rewriting the whole class string, add and remove just the highlight class.

What the code does

classList.add("active") adds a class without removing existing classes. classList.remove("active") removes only that class. classList.contains("active") returns a boolean so your code can report the current state. CSS defines what .active looks like; JavaScript only chooses whether the element has it. As with the checkbox in the previous section, addEventListener("click", () => { ... }) waits for a button click before running the code inside. The events section will unpack this pattern further; for now, use it to see the class changes.

In script.js, this is the important part of the already-working preview:

javascript
const programme = document.querySelector("#programme");
const programmeStatus = document.querySelector("#programme-status");
document.querySelector("#mark-programme").addEventListener("click", () => {
  programme.classList.add("active");
  programmeStatus.textContent = `Marked: ${programme.classList.contains("active")}`;
});
document.querySelector("#clear-programme").addEventListener("click", () => {
  programme.classList.remove("active");
  programmeStatus.textContent = `Marked: ${programme.classList.contains("active")}`;
});

Try it in the preview

Click Mark: the programme turns green and the status says true. Click Clear: the green highlight disappears and the status says false. The original note class remains in both states.

Which method answers a yes/no question about a class? contains. Which two methods change it? add and remove.

The next lesson gives you a different page to build from a starter.

Loading editor…
READY
intercourses
javascript