combobox: implement loading state w/ new listeners & lazy mode

src/lib/Combobox.svelte

@@ -27,6 +27,7 @@
 	import { generateIdentifier } from './util';
 	import type { ClassValue } from 'svelte/elements';
 	import { matchSorter } from 'match-sorter';
+	import Spinner from './Spinner.svelte';
 
 	interface Props {
 		name?: string;
@@ -39,14 +40,21 @@
 		invalidMessage?: string | null;
 		label?: string;
 		placeholder?: string;
+		/**
+		 * enables loading spinner and fallback text if no items are found. may be changed
+		 * internally if lazy is enabled. loading is, however, not bindable, so don't expect
+		 * any internal changes to be propagated outward.
+		 */
 		loading?: boolean;
+		/** applies the loading state on first interaction */
+		lazy?: boolean;
 		notFoundMessage?: string;
 		class?: ClassValue | null | undefined;
 		use?: () => void;
 		onvalidate?: (e: InputValidatorEvent) => void;
 		onchange?: (item: ComboboxOption) => void;
 		onsearch?: (query: string) => boolean | void;
-		onscroll?: (detail: { event: MouseEvent; top: boolean; false: boolean }) => void;
+		onscroll?: (detail: { event: UIEvent; top: boolean; bottom: boolean }) => void;
 	}
 
 	let {
@@ -61,6 +69,7 @@
 		label,
 		placeholder,
 		loading = false,
+		lazy = false,
 		notFoundMessage = 'No results found',
 		class: classValue,
 		use,
@@ -82,22 +91,28 @@
 	let pickerContainer = $state<HTMLDivElement | null>(null);
 
 	/** stores options filtered according to search value */
-	const filteredItems = $derived(
+	const filteredItems = $derived.by(() => {
-		searchValue === ''
+		const arr = matchSorter(options, searchValue, { keys: [(item) => getLabel(item)] });
-			? options
+		// if (loading) {
-			: matchSorter(options, searchValue, { keys: [(item) => getLabel(item)] })
+		// arr.push({ value: 'loading', label: 'Loading more...', disabled: true });
-	);
+		// }
+		return arr;
+	});
 
-	/** stores currently highlighted option (according to hover state or keyboard navigation) */
+	/** stores currently highlighted option (according to keyboard navigation or default item) */
 	let highlighted = $derived.by((): ComboboxOption | undefined => {
 		if (filteredItems.length === 0) return undefined;
 		if (value !== undefined && filteredItems.find((v) => v.value === value?.value)) return value;
-		return filteredItems[0];
+		if (!filteredItems[0]?.disabled) return filteredItems[0];
 	});
 
 	/** controls whether an icon should be displayed */
 	let iconVisible = $derived.by(() => {
-		return (open && highlighted && highlighted.icon) || (value && value.icon && searchValue === '');
+		return (
+			(open && highlighted && highlighted.icon) ||
+			(value && value.icon && searchValue === '') ||
+			loading
+		);
 	});
 
 	/** controls whether the highlighted option should be used in the selection preview  */
@@ -108,10 +123,37 @@
 	const validateOpts: ValidatorOptions = { required };
 
 	/** returns the index of the highlighted item in filteredItems */
-	const getHightlightedID = () => {
+	const getHighlightedIndex = () => {
 		if (highlighted === undefined) return -1;
 		return filteredItems.findIndex((item) => item.value === highlighted?.value);
 	};
+	/** returns the next or previous available item in filteredItems */
+	const getLogicalOption = (startIndex: number, step: number): ComboboxOption | undefined => {
+		const constrain = (index: number) => {
+			if (index < 0) index = filteredItems.length - 1;
+			else if (index >= filteredItems.length) index = 0;
+			return index;
+		};
+
+		let index = constrain(startIndex + step);
+		while (index >= 0 && index < filteredItems.length) {
+			const option = filteredItems[index];
+			if (option.disabled) {
+				index = constrain(index + step);
+				continue;
+			}
+			return option;
+		}
+		return undefined;
+	};
+	/** returns the next available item in filteredItems */
+	const getNextOption = () => {
+		return getLogicalOption(getHighlightedIndex(), 1);
+	};
+	/** returns the previous available item in filteredItems */
+	const getPrevOption = () => {
+		return getLogicalOption(getHighlightedIndex(), -1);
+	};
 
 	/** action to set the minimum width of the combobox based on the number of options */
 	const minWidth: Action<HTMLDivElement, { options: ComboboxOption[] }> = (
@@ -242,11 +284,12 @@
 		});
 	}
 
-	// when the picker is opened, update its position
+	// when the picker is opened, update its position and check if lazy
 	// when the picker is closed, clear any search value (next time it opens, all options will be shown)
 	// when the picker is closed, reset highlighted to the currently selected value (if any)
 	$effect(() => {
 		if (open) {
+			if (lazy) loading = true;
 			updatePickerRect();
 			scrollToHighlighted();
 		} else {
@@ -288,6 +331,7 @@
 	});
 </script>
 
+<!-- Combobox picker -->
 <Portal target="body">
 	{#if open}
 		<div
@@ -309,6 +353,16 @@
 					searchInput?.focus();
 				}
 			}}
+			onscroll={(e) => {
+				if (!onscroll) return;
+				const target = e.target as HTMLDivElement;
+				if (!target) return;
+
+				const margin = 10; // 10px margin for top & bottom
+				const atTop = target.scrollTop < margin;
+				const atBottom = target.scrollTop + target.clientHeight > target.scrollHeight - margin;
+				onscroll({ event: e, top: atTop, bottom: atBottom });
+			}}
 			tabindex="0"
 		>
 			{#each filteredItems as item, i (i + item.value)}
@@ -321,10 +375,12 @@
 						'picker-item options-center mb-0.5 flex min-h-10 flex-wrap py-2.5 pr-1.5 pl-5',
 						'rounded-sm text-sm capitalize outline-hidden select-none',
 						'hover:bg-sui-accent-500/30 dark:hover:bg-sui-accent-700/30',
-						item.value === highlighted?.value && 'bg-sui-accent-500/80 dark:bg-sui-accent-700/80'
+						item.value === highlighted?.value && 'bg-sui-accent-500/80 dark:bg-sui-accent-700/80',
+						item.disabled && 'cursor-not-allowed opacity-50'
 					]}
 					role="option"
 					onclick={() => {
+						if (item.disabled) return;
 						value = item;
 						open = false;
 						searchInput?.focus();
@@ -358,7 +414,13 @@
 					{/if}
 				</div>
 			{:else}
-				<span class="block px-5 py-2 text-sm">{notFoundMessage}</span>
+				<span class="block px-5 py-2 text-sm">
+					{#if loading}
+						Loading...
+					{:else}
+						{notFoundMessage}
+					{/if}
+				</span>
 			{/each}
 		</div>
 	{/if}
@@ -396,6 +458,7 @@
 	{/if}
 </div>
 
+<!-- Search input box -->
 {#snippet searchInputBox(caret: boolean = true)}
 	<div class="relative">
 		{#if iconVisible}
@@ -405,7 +468,9 @@
 				]}
 				transition:scale
 			>
-				{#if useHighlighted && highlighted?.icon}
+				{#if loading}
+					<Spinner class="stroke-sui-accent!" size="1em" />
+				{:else if useHighlighted && highlighted?.icon}
 					{@render highlighted.icon(highlighted)}
 				{:else if value?.icon}
 					{@render value.icon(value)}
@@ -435,7 +500,7 @@
 				if (!searchInput) return;
 
 				if (e.key === 'Tab' || e.key === 'Enter') {
-					if (open && highlighted && highlighted.value !== value?.value) {
+					if (open && highlighted && !highlighted.disabled && highlighted.value !== value?.value) {
 						value = highlighted;
 						onchange?.(highlighted);
 					}
@@ -460,16 +525,10 @@
 				}
 
 				if (e.key === 'ArrowDown') {
-					const nextIndex = getHightlightedID() + 1;
+					highlighted = getNextOption();
-					if (nextIndex < filteredItems.length) {
-						highlighted = filteredItems[nextIndex];
-					}
 					return;
 				} else if (e.key === 'ArrowUp') {
-					const prevIndex = getHightlightedID() - 1;
+					highlighted = getPrevOption();
-					if (prevIndex >= 0) {
-						highlighted = filteredItems[prevIndex];
-					}
 					return;
 				}
 			}}
@@ -477,6 +536,7 @@
 				if (!searchInput) return;
 				searchValue = searchInput.value;
 				searching = true;
+				onsearch?.(searchValue);
 			}}
 			use={() => {
 				conditionalUse();

src/routes/+page.svelte

@@ -120,10 +120,24 @@
 <div class="component">
 	<p class="title">Combobox</p>
 
+	<InputGroup>
 		<Combobox
 			name="example-combobox"
 			label="Select an option"
 			placeholder="Choose..."
+			options={[
+				{ value: 'option1', label: 'Option 1' },
+				{ value: 'option2', label: 'Option 2' },
+				{ value: 'option3', label: 'Option 3', disabled: true }
+			]}
+			onchange={(e) => console.log('Selected:', e.value)}
+			onvalidate={(e) => console.log('Validation:', e.detail)}
+		/>
+
+		<Combobox
+			loading
+			label="Loading state combobox"
+			placeholder="Choose..."
 			options={[
 				{ value: 'option1', label: 'Option 1' },
 				{ value: 'option2', label: 'Option 2' },
@@ -132,6 +146,9 @@
 			onchange={(e) => console.log('Selected:', e.value)}
 			onvalidate={(e) => console.log('Validation:', e.detail)}
 		/>
+
+		<Combobox label="Lazy combobox" placeholder="Choose..." options={[]} lazy />
+	</InputGroup>
 </div>
 
 <div class="component">