js: Simplify indexing arrays from the end with Array#at.

https://github.com/tc39/proposal-relative-indexing-method

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

frontend_tests/node_tests/narrow_local.js

@@ -54,7 +54,7 @@ function test_with(fixture) {
         },
         last: () => {
             assert.notEqual(fixture.all_messages, undefined);
-            return fixture.all_messages[fixture.all_messages.length - 1];
+            return fixture.all_messages.at(-1);
         },
     };
 

frontend_tests/zjsunit/mdiff.js

@@ -109,10 +109,7 @@ function diff_strings(string_0, string_1) {
             output_lines.push(line);
         } else if (line.startsWith("?")) {
             changes_list = parse_questionmark_line(line);
-            output_lines[output_lines.length - 1] = apply_color(
+            output_lines.push(apply_color(output_lines.pop(), changes_list));
-                output_lines[output_lines.length - 1],
-                changes_list,
-            );
         } else {
             output_lines.push(line);
         }

static/js/drafts.js

@@ -470,7 +470,7 @@ function drafts_initialize_focus(event_name) {
     let draft_element;
     if (event_name === "up_arrow") {
         draft_element = document.querySelectorAll(
-            '[data-draft-id="' + draft_id_arrow[draft_id_arrow.length - 1] + '"]',
+            '[data-draft-id="' + draft_id_arrow.at(-1) + '"]',
         );
     } else if (event_name === "down_arrow") {
         draft_element = document.querySelectorAll('[data-draft-id="' + draft_id_arrow[0] + '"]');
@@ -565,7 +565,7 @@ export function drafts_handle_events(e, event_key) {
         if (document.activeElement.parentElement.hasAttribute("data-draft-id")) {
             restore_draft(focused_draft_id);
         } else {
-            const first_draft = draft_id_arrow[draft_id_arrow.length - 1];
+            const first_draft = draft_id_arrow.at(-1);
             restore_draft(first_draft);
         }
     }

static/js/emoji_picker.js

@@ -563,7 +563,7 @@ export function emoji_select_tab(elt) {
     // Handles the corner case of the last category being
     // smaller than half of the emoji picker height.
     if (elt_height + scrolltop === scrollheight) {
-        currently_selected = section_head_offsets[section_head_offsets.length - 1].section;
+        currently_selected = section_head_offsets.at(-1).section;
     }
     // Handles the corner case of the scrolling back to top.
     if (scrolltop === 0) {

static/js/floating_recipient_bar.js

@@ -85,7 +85,7 @@ export function first_visible_message(bar) {
     }
 
     // If none of the messages are visible, just take the last message.
-    return $(messages[messages.length - 1]);
+    return messages.last();
 }
 
 export function get_date(elem) {

static/js/message_fetch.js

@@ -440,7 +440,7 @@ export function initialize(home_view_loaded) {
         // If we fall through here, we need to keep fetching more data, and
         // we'll call back to the function we're in.
         const messages = data.messages;
-        const latest_id = messages[messages.length - 1].id;
+        const latest_id = messages.at(-1).id;
 
         load_messages({
             anchor: latest_id,

static/js/message_list_data.js

@@ -39,7 +39,7 @@ export class MessageListData {
     }
 
     last() {
-        return this._items[this._items.length - 1];
+        return this._items.at(-1);
     }
 
     select_idx() {

static/js/message_list_view.js

@@ -344,9 +344,7 @@ export class MessageListView {
                     current_group,
                     current_group.message_containers[0],
                 );
-                current_group.message_containers[
+                current_group.message_containers.at(-1).include_footer = true;
-                    current_group.message_containers.length - 1
-                ].include_footer = true;
                 new_message_groups.push(current_group);
             }
         };
@@ -1212,7 +1210,7 @@ export class MessageListView {
         for (const message_container of message_containers) {
             if (
                 current_group.length === 0 ||
-                same_recipient(current_group[current_group.length - 1], message_container)
+                same_recipient(current_group.at(-1), message_container)
             ) {
                 current_group.push(message_container);
             } else {

static/js/portico/integrations_dev_panel.js

@@ -74,8 +74,7 @@ function get_selected_integration_name() {
 }
 
 function get_fixture_format(fixture_name) {
-    const pieces = fixture_name.split(".");
+    return fixture_name.split(".").at(-1);
-    return pieces[pieces.length - 1];
 }
 
 function get_custom_http_headers() {

static/js/search_suggestion.js

@@ -641,7 +641,6 @@ export function get_search_result(base_query, query) {
     }
 
     const person_suggestion_ops = ["sender", "pm-with", "from", "group-pm"];
-    const search_operators_len = search_operators.length;
 
     // Handle spaces in person name in new suggestions only. Checks if the last operator is 'search'
     // and the second last operator in search_operators is one out of person_suggestion_ops.
@@ -650,11 +649,11 @@ export function get_search_result(base_query, query) {
     // is an email of a user, both of these operators remain unchanged. Otherwise search operator
     // will be deleted and new last will become {operator:'sender', operand: 'Ted sm`....}.
     if (
-        search_operators_len > 1 &&
+        search_operators.length > 1 &&
         last.operator === "search" &&
-        person_suggestion_ops.includes(search_operators[search_operators_len - 2].operator)
+        person_suggestion_ops.includes(search_operators.at(-2).operator)
     ) {
-        const person_op = search_operators[search_operators_len - 2];
+        const person_op = search_operators.at(-2);
         if (!people.reply_to_to_user_ids_string(person_op.operand)) {
             last = {
                 operator: person_op.operator,
@@ -662,11 +661,11 @@ export function get_search_result(base_query, query) {
                 negated: person_op.negated,
             };
             if (page_params.search_pills_enabled) {
-                all_operators[all_operators.length - 2] = last;
+                all_operators.splice(-2);
-                all_operators.splice(-1, 1);
+                all_operators.push(last);
             }
-            search_operators[search_operators_len - 2] = last;
+            search_operators.splice(-2);
-            search_operators.splice(-1, 1);
+            search_operators.push(last);
         }
     }
 

static/js/stats/stats.js

@@ -73,7 +73,7 @@ function update_last_full_update(end_times) {
         return;
     }
 
-    last_full_update = Math.min(last_full_update, end_times[end_times.length - 1]);
+    last_full_update = Math.min(last_full_update, end_times.at(-1));
     const update_time = new Date(last_full_update * 1000);
     const locale_date = update_time.toLocaleDateString("en-US", {
         year: "numeric",
@@ -253,7 +253,7 @@ function populate_messages_sent_over_time(data) {
             dates,
             values,
             last_value_is_partial: !is_boundary(
-                new Date(start_dates[start_dates.length - 1].getTime() + 60 * 60 * 1000),
+                new Date(start_dates.at(-1).getTime() + 60 * 60 * 1000),
             ),
         };
     }
@@ -386,7 +386,7 @@ function compute_summary_chart_data(time_series_data, num_steps, labels_) {
         }
         let sum = 0;
         for (let i = 1; i <= num_steps; i += 1) {
-            sum += array[array.length - i];
+            sum += array.at(-i);
         }
         data.set(key, sum);
     }
@@ -939,7 +939,7 @@ function populate_messages_read_over_time(data) {
             dates,
             values,
             last_value_is_partial: !is_boundary(
-                new Date(start_dates[start_dates.length - 1].getTime() + 60 * 60 * 1000),
+                new Date(start_dates.at(-1).getTime() + 60 * 60 * 1000),
             ),
         };
     }

static/js/upload.js

@@ -242,7 +242,7 @@ export function setup_upload(config) {
             return;
         }
         const split_uri = uri.split("/");
-        const filename = split_uri[split_uri.length - 1];
+        const filename = split_uri.at(-1);
         if (config.mode === "compose" && !compose_state.composing()) {
             compose_actions.start("stream");
         }

static/shared/js/fenced_code.js

@@ -209,18 +209,18 @@ export function process_fenced_code(content) {
     handler_stack.push(current_handler);
 
     for (const line of input) {
-        const handler = handler_stack[handler_stack.length - 1];
+        const handler = handler_stack.at(-1);
         handler.handle_line(line);
     }
 
     // Clean up all trailing blocks by letting them
     // insert closing fences
     while (handler_stack.length !== 0) {
-        const handler = handler_stack[handler_stack.length - 1];
+        const handler = handler_stack.at(-1);
         handler.done();
     }
 
-    if (output.length > 2 && output[output.length - 2] !== "") {
+    if (output.length > 2 && output.at(-2) !== "") {
         output.push("");
     }