Personal Catalogue: PHP & MySQL — Chapter 4, Exercise 2
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TASK
Add the same label-switching script to edit_item.php, and confirm
that opening the edit form for an existing DVD shows "Director" and
"Region code" correctly pre-labeled on page load, before any dropdown
change happens.

SOLUTION

The markup and script additions are identical to add_item.php's own
version from Exercise 1 — the same ids, the same data-name attributes,
the same two label maps, and the same updateLabels() function.

The one detail that matters specifically for edit_item.php: the
dropdown's own currently-selected <option> already carries the
'selected' attribute from Chapter 3's Exercise 2 (comparing
$type['id'] against $item['item_type_id']), so when the page first
loads, select.selectedIndex already points at the correct option
before any JavaScript runs at all.

The critical line from the chapter is the one that makes this actually
work on page load rather than only after a manual change:

    select.addEventListener('change', updateLabels);
    // Run once on load too, in case a type is already selected
    // (e.g. the edit form, where an item's own type is pre-chosen).
    updateLabels();

That final updateLabels() call — run immediately, not just registered
as a listener — is what makes the labels correct the very first time
the page renders.

To confirm: open edit_item.php?id=3 (the DVD, "The Matrix," from
Chapter 3's own Exercise 1) directly. Without touching the dropdown at
all, the labels should already read "Director:" and "Region code:" —
proof the script ran once immediately on load, using the dropdown's
own already-selected option, rather than waiting for a 'change' event
that never actually fires if the user doesn't touch the dropdown.

WHY THIS WORKS AS AN ANSWER
----------------------------
It identifies the specific line (the immediate updateLabels() call,
not just the event listener) responsible for the pre-filled-on-load
behavior the exercise asks to confirm, and gives a concrete test (load
the DVD's edit page and check the labels with zero interaction) that
would fail if that line were missing.