eslint: Fix unicorn/prefer-at.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

web/src/search_suggestion.js

@@ -720,7 +720,7 @@ export function get_search_result(base_query, query) {
     const search_operators = Filter.parse(query);
     let last = {operator: "", operand: "", negated: false};
     if (search_operators.length > 0) {
-        last = search_operators.slice(-1)[0];
+        last = search_operators.at(-1);
     } else if (page_params.search_pills_enabled) {
         // We push an empty term so that we can get suggestions
         // on the empty string based on the base query which is

web/src/settings_profile_fields.js

@@ -182,7 +182,7 @@ function get_value_for_new_option(container) {
         existing_option_values.push(Number.parseInt($(this).attr("data-value"), 10));
     });
     existing_option_values.sort();
-    return existing_option_values[existing_option_values.length - 1] + 1;
+    return existing_option_values.at(-1) + 1;
 }
 
 function create_choice_row(container) {

web/src/upload.js

@@ -344,7 +344,7 @@ export function setup_upload(config) {
         // TODO: Ideally, we'd be using the `.error()` hook or
         // something, not parsing error message strings.
         const infoList = uppy.getState().info;
-        const info = infoList[infoList.length - 1];
+        const info = infoList.at(-1);
         if (info.type === "error" && info.message === "No Internet connection") {
             // server_events already handles the case of no internet.
             return;