Try something like:
import wixData from 'wix-data';
let dataset1Lists;
let isDataset2Ready = false;
$w.onReady(() => {
$w('#dataset1').onReady(() => {
$w('#dataset1').getItems(0, 1000).then(r => {
dataset1Lists = r.items.map(e => e.list);
filterDataset2();
});
});
$w('#dataset2').onReady(() => {
isDataset2Ready = true;
filterDataset2();
});
});
function filterDataset2() {
if (dataset1Lists && isDataset2Ready) {
if (dataset1Lists.length > 0) {
let filter = wixData.filter();
dataset1Lists.forEach(e => filter = filter.ne('list', e));
$w('#dataset2').setFilter(filter);
}
}
}