Hi there,
You should not use the $w.at() inside a repeater scoop, you should only use it with the global selector ($w), so you should either do this:
$w('#clickBtn').onClick(event => {
const $item = $w.at(event.context);
if ($item('#container').hidden) {
$item('#container').show();
} else {
$item('#container').hide();
}
})
Or this:
$w('#repeater').onItemReady(($item, data) => {
if ($item('#container').hidden) {
$item('#container').show();
} else {
$item('#container').hide();
}
})
Bot not both methods.
Give it a shot and let me know if it works for you.