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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

Boolean attributes and DOM properties

A garden tour booking button should stay unavailable until a visitor agrees to the meeting instructions. The checkbox controls whether the button can be used.

Presence, not a string value

In HTML, disabled and checked are boolean attributes. Their presence means true, even if the markup says disabled="false"; only leaving the attribute out means false. In JavaScript, use the corresponding boolean properties: button.disabled and checkbox.checked. Assign true or false, not the strings "true" or "false". Changing button.disabled reflects in its HTML attribute, but changing a checkbox's current .checked state does not rewrite its default checked attribute. element.hasAttribute("disabled") reports whether the button attribute is present; unlike getAttribute, it returns a boolean. The checkbox's .checked property reports its current state, whereas getAttribute("checked") reads the original/default markup attribute and does not reliably track later clicks.

This is the first completed click/change interaction in this part of the course. addEventListener("change", updateBooking) asks the browser to call the function whenever the checkbox changes; the separate updateBooking() call sets the initial state before any interaction. Events get a dedicated section later. The working script.js updates both the control and a plain-language message:

javascript
const consent = document.querySelector("#tour-consent");
const reserve = document.querySelector("#reserve-tour");
const status = document.querySelector("#booking-status");
function updateBooking() {
  reserve.disabled = !consent.checked;
  status.textContent = reserve.hasAttribute("disabled")
    ? "Agree to the tour instructions first."
    : "Tour booking is ready.";
}
consent.addEventListener("change", updateBooking);
updateBooking();

The initial call matters: without it, the message and control might disagree before anyone interacts. A native disabled button cannot receive a click, so no extra click guard is needed here.

Try it in the preview

Initially the button is disabled and the instruction appears. Check the box: the button becomes available and the message changes. Uncheck it to restore the disabled state. In index.html, try replacing disabled with disabled="false" and Run: the button is still disabled until the checkbox is checked. Restore the original markup afterward. Next, apply this pattern to another kind of sign-up.

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