frappe.ui.form.on(cur_frm.doctype, {
    'onload_post_render': function(frm) {
        frm.fields_dict.items.grid.wrapper.on('focus', 'input[data-fieldname="item_name"][data-doctype="Sales Invoice Item"]', function(e) {
            console.log(e.type);
        });
    }
});