feat: accessible tab kbd navigation

src/lib/components/tab.svelte

@@ -1,19 +1,95 @@
 <script lang="ts">
+    import { goto } from '$app/navigation';
     import { trackEvent } from '$lib/actions/analytics';
+    import { last } from '$lib/helpers/array';
+    import { getElementDir } from '$lib/helpers/style';
+    import { waitUntil } from '$lib/helpers/waitUntil';
 
     export let selected = false;
     export let href: string = null;
     export let event: string = null;
 
-    function track() {
-        if (!event) return;
-        trackEvent(`click_select_tab_${event}`);
+    async function handleClick(e: Event) {
+        if (event) {
+            trackEvent(`click_select_tab_${event}`);
+        }
+
+        if (href) {
+            let el = e.target as HTMLElement;
+            if (el.tagName !== 'A') {
+                el = el.closest('a');
+            }
+
+            await goto(href);
+            await waitUntil(() => {
+                console.log('tickUntil', el);
+                return el.classList.contains('is-selected');
+            }, 1000);
+            el.focus();
+        }
+    }
+
+    const keysMap = {
+        ltr: {
+            next: 'ArrowRight',
+            prev: 'ArrowLeft'
+        },
+        rtl: {
+            next: 'ArrowLeft',
+            prev: 'ArrowRight'
+        }
+    };
+
+    function handleKeyDown(e: KeyboardEvent) {
+        const tabBtn = e.target as HTMLElement;
+        const tabItem = tabBtn.closest('.tabs-item') as HTMLElement;
+        const tabsList = tabItem.closest('.tabs') as HTMLElement;
+        const tabItems = Array.from(tabsList.querySelectorAll('.tabs-item'));
+        const currentIdx = tabItems.indexOf(tabItem);
+
+        const dir = getElementDir(tabsList);
+
+        switch (e.key) {
+            case 'Home': {
+                e.preventDefault();
+                const firstTabBtn = tabItems[0].querySelector('.tabs-button') as HTMLElement;
+                firstTabBtn.focus();
+                break;
+            }
+            case 'End': {
+                e.preventDefault();
+                const lastTabBtn = last(tabItems).querySelector('.tabs-button') as HTMLElement;
+                lastTabBtn.focus();
+                break;
+            }
+            case keysMap[dir].next: {
+                e.preventDefault();
+                const nextIdx = currentIdx === tabItems.length - 1 ? 0 : currentIdx + 1;
+                const nextTabBtn = tabItems[nextIdx].querySelector('.tabs-button') as HTMLElement;
+                nextTabBtn.focus();
+                break;
+            }
+            case keysMap[dir].prev: {
+                e.preventDefault();
+                const prevIdx = currentIdx === 0 ? tabItems.length - 1 : currentIdx - 1;
+                const prevTabBtn = tabItems[prevIdx].querySelector('.tabs-button') as HTMLElement;
+                prevTabBtn.focus();
+                break;
+            }
+        }
     }
 </script>
 
 <li class="tabs-item">
     {#if href}
-        <a class="tabs-button" {href} class:is-selected={selected} on:click={track}>
+        <a
+            class="tabs-button"
+            {href}
+            class:is-selected={selected}
+            on:click={handleClick}
+            tabindex={selected ? 0 : -1}
+            on:keydown={handleKeyDown}
+            role="tab">
             <span class="text"><slot /></span>
         </a>
     {:else}
@@ -22,7 +98,10 @@
             class="tabs-button"
             class:is-selected={selected}
             on:click|preventDefault
-            on:click={track}>
+            on:click={handleClick}
+            tabindex={selected ? 0 : -1}
+            on:keydown={handleKeyDown}
+            role="tab">
             <span class="text"><slot /></span>
         </button>
     {/if}

src/lib/helpers/style.ts

@@ -0,0 +1,16 @@
+type Direction = 'rtl' | 'ltr';
+
+function isDirection(dir: string): dir is Direction {
+    return dir === 'rtl' || dir === 'ltr';
+}
+
+function parseDirection(dir: string): Direction {
+    return isDirection(dir) ? dir : 'ltr';
+}
+
+export function getElementDir(el: HTMLElement): Direction {
+    if (window.getComputedStyle) {
+        return parseDirection(window.getComputedStyle(el, null).getPropertyValue('direction'));
+    }
+    return parseDirection(el.style.direction);
+}

src/lib/helpers/waitUntil.ts

@@ -0,0 +1,14 @@
+export async function waitUntil(condition: () => boolean, timeout = 1000) {
+    return new Promise((resolve, reject) => {
+        const start = Date.now();
+        const interval = setInterval(() => {
+            if (condition()) {
+                clearInterval(interval);
+                resolve(undefined);
+            } else if (Date.now() - start > timeout) {
+                clearInterval(interval);
+                reject(new Error('Timeout'));
+            }
+        }, 10);
+    });
+}

tests/unit/components/tab.test.ts

@@ -6,12 +6,12 @@ import { Tab } from '../../../src/lib/components';
 test('shows tab', () => {
     const { getByRole } = render(Tab);
 
-    expect(getByRole('button')).toBeInTheDocument();
+    expect(getByRole('tab')).toBeInTheDocument();
 });
 test('shows tab - is selected', () => {
     const { getByRole } = render(Tab, { selected: true });
 
-    expect(getByRole('button')).toHaveClass('is-selected');
+    expect(getByRole('tab')).toHaveClass('is-selected');
 });
 
 test('shows tab - is link', () => {
@@ -23,7 +23,7 @@ test('shows tab - is link', () => {
 
 test('shows tab - on:click', async () => {
     const { getByRole, component } = render(Tab);
-    const tab = getByRole('button');
+    const tab = getByRole('tab');
     const callback = vi.fn();
     component.$on('click', callback);