Automatically link arxiv pdf in zotero

zotero_arxiv.js

var arxiv_url_pattern = "arxiv.org/abs/";
const LINK_MODE_LINKED_URL = 3;
var s = new Zotero.Search();
s.libraryID = ZoteroPane.getSelectedLibraryID();
s.addCondition('url', 'contains', arxiv_url_pattern);
var ids = await s.search();
if (!ids.length) {
    return "No items found";
} else {
    Zotero.warn("Find " + ids.length + " items");
}
await Zotero.DB.executeTransaction(async function () {
    for (let id of ids) {
        let item = await Zotero.Items.getAsync(id);
        Zotero.warn("start: " + item.getField("title"));
        try {
            if (item.getAttachments().length > 0) {
                Zotero.warn("already have attachment, skip");
                continue;
            }
        } catch (error) {
            // attachment types.
            Zotero.warn("invalid item type, skip " + error);
            continue;
        }
        let url = item.getField("url");
        let file_url = url.replace("arxiv.org/abs/", "arxiv.org/pdf/") + ".pdf";
        await Zotero.Attachments.addPDFFromURLs(item, [file_url]);
        await item.save();
        Zotero.warn("done: " + item.getField("title"));
    }
});
return ids.length + " item(s) updated";