Scout — API Reference

API Overview

Symbol	Purpose	Execution mode	Common gotcha
`createIndex()`	Build trigram index from an item array	Sync	Index is built at call time — pass all initial items
`ScoutIndex.search()`	Query the index, returns scored + highlighted results	Sync	Empty query returns all items with `score = 1`
`ScoutIndex.add()`	Add one item to the index	Sync	No-op if same reference already indexed
`ScoutIndex.remove()`	Remove one item by reference	Sync	No-op for unknown references
`ScoutIndex.reindex()`	Re-index a mutated item in-place; preserves order	Sync	Call after mutating item properties; no-op if not in index
`ScoutIndex.setItems()`	Reconcile a refreshed corpus in one mutation	Sync	Uses reference identity; duplicate references collapse
`ScoutIndex.items`	All indexed items in insertion order	Sync	Returns a new array snapshot each call
`ScoutIndex.revision`	Monotonic counter incremented after each mutation	Sync	Use as a cache-busting token for external result caches
`ScoutIndex.onMutate()`	Subscribe to changed index mutations	Sync	A changed `setItems()` reconciliation emits once; no-ops emit nothing
`createSearch()`	Reactive search state backed by a `ScoutIndex`	Sync	Requires `@vielzeug/ripple` — dispose when done
`createReactiveSearch()`	One-call index + reactive search state	Sync	Exposes `.index` for incremental mutations
`findMatchRanges()`	Compute match ranges for a text + query pair	Sync	Returns sorted, non-overlapping `[start, end]` ranges
`highlight()`	Split text into highlighted/unhighlighted fragments	Sync	Ranges must be sorted and non-overlapping
`highlightField()`	Highlight a named field from a `SearchResult`	Sync	Shorthand for the `matches.find(…).ranges → highlight()` pattern
`toSearchMatcher()`	Adapt `ScoutIndex` to Sourcerer's `match` callback	Sync	Recomputes cached query matches after index mutation
`toFilterPredicate()`	Snapshot predicate from a one-time query	Sync	Re-call when query or corpus changes
`segmentWords()`	Split unsegmented-script text (CJK, Thai, ...) into words	Sync	Uses native `Intl.Segmenter` — not applied inside `tokenize()` itself (see Pitfalls)
`debugSearch()`	Log a `SearchState`'s query/results transitions	Sync	Import from `@vielzeug/scout/devtools`, not the main entry point

Package Entry Point

Import	Purpose
`@vielzeug/scout`	All exports — index/search/highlighting/adapters, `ScoutConfigurationError`, `ScoutDisposedError`, `ScoutError`, and all types
`@vielzeug/scout/devtools`	`debugSearch` — reactive search state logger (dev only)

`createIndex(items, options)`

Builds a trigram inverted index from items. Construction is O(corpus × field_length); subsequent search() calls are O(candidates).

function createIndex<T>(items: T[], options: ScoutIndexOptions<T>): ScoutIndex<T>

Parameters

Param	Type	Description
`items`	`T[]`	Initial corpus to index.
`options.fields`	`ReadonlyArray<FieldDef<T>>`	Fields to index. Required; at least one entry.
`options.threshold`	`number`	Finite overlap score in `0..1` (default `0.2`).
`options.limit`	`number`	Finite non-negative integer max results (default `50`).
`options.minQueryLength`	`number`	Finite positive integer min chars before trigram scoring; shorter queries use O(n) containment scan (default `3`).

Example

import { createIndex } from '@vielzeug/scout';

const products = [
  { sku: 'WGT-001', title: 'Widget Pro' },
  { sku: 'GAD-002', title: 'Gadget Plus' },
];

const index = createIndex(products, {
  fields: [
    { field: 'title', weight: 2 },
    { field: 'sku' },
  ],
  threshold: 0.25,
  limit: 20,
});

`ScoutIndex<T>`

Returned by createIndex().

`.search(query, options?)`

search(query: string, options?: SearchConstraints): SearchResult<T>[]

Returns results sorted by score descending. Empty query returns all items with score = 1. Results below threshold are excluded; at most limit results are returned.

const results = index.search('alice');
// [{ item, score, matches }]

`.add(item)`

Adds item to the index. No-op if the same reference is already indexed. O(field_length).

`.remove(item)`

Removes item by reference equality. No-op if not found. O(field_length).

`.reindex(item)`

Re-reads the item's current field values and rebuilds its index entry in-place, updating only fields whose values changed. Preserves insertion order. No-op if the item is not in the index.

item.name = 'new name';
index.reindex(item);

`.setItems(items)`

setItems(items: readonly T[]): void

Reconciles the index to a refreshed corpus in one mutation. Existing references are reindexed, missing references are removed, added references are indexed, and incoming first-occurrence order becomes index order. Duplicate references collapse to one item. Calls onMutate() once when indexed values, membership, or order changes.

index.setItems(latestUsers);

`.size`

number — current number of indexed items.

`.items`

readonly T[] — all indexed items in insertion order. Returns a new array snapshot each call.

const all = index.items;

`.onMutate(listener)`

onMutate(listener: () => void): () => void

Subscribes listener to run after every changed add() / remove() / reindex() / setItems() operation. No-ops, including unchanged bulk reconciliation, do not fire it. A changed setItems() reconciliation fires once. createSearch() uses this internally to keep results in sync with index mutations; most callers building on createIndex() directly will not need it.

const unsubscribe = index.onMutate(() => {
  console.log(`Index changed — now ${index.size} items`);
});

index.add(newUser); // logs "Index changed — now 6 items"
unsubscribe();

`.revision`

number — monotonically increasing counter, incremented after every changed add() / remove() / reindex() / setItems() operation. Use as a cache-busting token when caching search results outside the index — toSearchMatcher() uses it for this purpose.

`createSearch(index, options?)`

Wraps a ScoutIndex in a reactive search state powered by @vielzeug/ripple signals.

function createSearch<T>(index: ScoutIndex<T>, options?: CreateSearchOptions): SearchState<T>

Parameters

Param	Type	Description
`options.debounce`	`number`	Finite non-negative integer milliseconds before query commit (default `200`). Pass `0` for immediate updates.
`options.limit`	`number`	Finite non-negative integer override of index-level limit.
`options.threshold`	`number`	Finite `0..1` override of index-level threshold.
`options.minQueryLength`	`number`	Finite positive integer override of index-level minimum query length.

Returns SearchState<T>

Member	Type	Description
`query`	`Signal<string>`	Writable search query. Set `.value` to trigger search.
`results`	`Computed<SearchResult<T>[]>`	Reactive results, updated after debounce.
`isSearching`	`Computed<boolean>`	`true` during the debounce window.
`clear()`	`() => void`	Resets query, cancels debounce, clears results synchronously.
`dispose()`	`() => void`	Releases all reactive subscriptions.
`[Symbol.dispose]()`	`() => void`	`using`-compatible disposal.

Example

import { createIndex, createSearch } from '@vielzeug/scout';
import { effect } from '@vielzeug/ripple';

const users = [{ name: 'Ada Lovelace' }, { name: 'Grace Hopper' }];
const index = createIndex(users, { fields: ['name'] });
const search = createSearch(index, { debounce: 150 });

effect(() => {
  console.log(search.results.value.map((result) => result.item.name));
});

search.query.value = 'ada';

`createReactiveSearch(items, options)`

Creates a ScoutIndex and a reactive SearchState in one call — the shorthand for createIndex + createSearch. Returns a ReactiveSearch<T> which extends SearchState<T> with a .index property for incremental mutations.

function createReactiveSearch<T>(
  items: T[],
  options: ScoutIndexOptions<T> & { debounce?: number },
): ReactiveSearch<T>

Parameters

Param	Type	Description
`items`	`T[]`	Initial corpus to index.
`options.fields`	`ReadonlyArray<FieldDef<T>>`	Fields to index. Required.
`options.debounce`	`number`	Finite non-negative integer debounce milliseconds (default `200`).
`options.threshold`	`number`	Finite overlap score in `0..1` (default `0.2`).
`options.limit`	`number`	Finite non-negative integer max results (default `50`).
`options.minQueryLength`	`number`	Finite positive integer min chars before trigram scoring (default `3`).

Returns ReactiveSearch<T> — all SearchState<T> members plus:

Member	Type	Description
`index`	`ScoutIndex<T>`	The underlying index for `add`, `remove`, `reindex`.

Example

import { createReactiveSearch } from '@vielzeug/scout';
import { effect } from '@vielzeug/ripple';

const users = [{ email: 'ada@example.com', name: 'Ada Lovelace' }];
const search = createReactiveSearch(users, {
  fields: [{ field: 'name', weight: 2 }, 'email'],
  debounce: 150,
});

effect(() => console.log(search.results.value.map((result) => result.item.name)));

search.index.add({ email: 'grace@example.com', name: 'Grace Hopper' });
search.dispose();

`findMatchRanges(text, query)`

Normalizes raw query with Scout's tokenizer, then computes sorted, non-overlapping literal ranges for each normalized token within text. Useful when you need to apply highlighting to a different string than the indexed field value (e.g. a truncated preview or a differently formatted display string).

function findMatchRanges(text: string, query: string): [number, number][]

Example

import { findMatchRanges, highlight } from '@vielzeug/scout';

const ranges = findMatchRanges('Alice Johnson', 'alice!');
// [[0, 5]]

const parts = highlight('Alice Johnson', ranges);
// [{ text: 'Alice', highlighted: true }, { text: ' Johnson', highlighted: false }]

Returns an empty array if either text or query is empty.

`highlight(text, ranges)`

Splits text into HighlightPart[] fragments based on ranges from FieldMatch.ranges.

function highlight(text: string, ranges: [number, number][]): HighlightPart[]

Example

import { highlight } from '@vielzeug/scout';

highlight('Hello World', [[0, 5]]);
// [{ text: 'Hello', highlighted: true }, { text: ' World', highlighted: false }]

Returns an empty array when text is empty. Returns a single unhighlighted part when ranges is empty.

`highlightField(result, field, text)`

Convenience shorthand that finds the match ranges for field in result.matches and calls highlight() in one step. Eliminates the manual result.matches.find(m => m.field === …).ranges lookup.

function highlightField<T>(result: SearchResult<T>, field: keyof T & string, text: string): HighlightPart[]

Example

import { createIndex, highlightField } from '@vielzeug/scout';

const users = [{ name: 'Alice Johnson' }];
const index = createIndex(users, { fields: ['name'] });

for (const result of index.search('alice')) {
  const parts = highlightField(result, 'name', result.item.name);
  console.log(parts.map((part) => part.highlighted ? `[${part.text}]` : part.text).join(''));
}

When the field has no match (e.g. the query matched via a different field), returns a single unhighlighted part.

`toSearchMatcher(index, options?)`

Returns an (item, query) => boolean matcher compatible with sourcerer's match option.

function toSearchMatcher<T>(index: ScoutIndex<T>, options?: SearchConstraints): (item: T, query: string) => boolean

One matching-item set is cached per query and index revision, so filtering does not repeat index work per item and stays current after index mutation.

import { createIndex, toSearchMatcher } from '@vielzeug/scout';
import { createLocalSource } from '@vielzeug/sourcerer';

const users = [{ email: 'ada@example.com', name: 'Ada Lovelace' }];
const index = createIndex(users, { fields: ['name', 'email'] });
const source = createLocalSource(users, { match: toSearchMatcher(index) });

`toFilterPredicate(index, query, options?)`

Returns a (item: T) => boolean predicate computed from a one-time query. Use with Array.filter or vault's query.filter().

function toFilterPredicate<T>(
  index: ScoutIndex<T>,
  query: string,
  options?: SearchConstraints,
): (item: T) => boolean

The predicate is a snapshot — re-call toFilterPredicate if the query or corpus changes.

import { createIndex, toFilterPredicate } from '@vielzeug/scout';

const products = [{ title: 'Widget Pro' }, { title: 'Gadget Plus' }];
const index = createIndex(products, { fields: ['title'] });
const results = products.filter(toFilterPredicate(index, 'widget'));

const top5 = products.filter(toFilterPredicate(index, 'widget', { limit: 5 }));

`segmentWords(text)`

Splits text into whitespace-joined word segments using the runtime's native Intl.Segmenter — no dependency beyond the platform API. Falls back to returning text unchanged where Intl.Segmenter isn't available.

function segmentWords(text: string): string

tokenize()'s trigram-based scoring already works on unsegmented scripts (Chinese, Japanese, Thai, ...) without this — trigrams are generated per-character, not per-word. segmentWords() is for findMatchRanges() / highlighting and the multi-word query semantics on SearchConstraints, which assume space-separated words. Not applied inside tokenize() itself — benchmarked at ~15x slower than the plain regex path for the common whitespace-delimited case, which would regress createIndex()'s construction cost for every caller, not just those indexing unsegmented scripts.

Example

import { createIndex, segmentWords } from '@vielzeug/scout';

const documents = [{ title: '日本語を勉強しています' }];
const index = createIndex(documents, {
  fields: [{ field: 'title', stringify: (value) => segmentWords(String(value)) }],
});

`debugSearch(search)`

debugSearch<T>(search: SearchState<T>): () => void

Logs query → isSearching → results transitions of a SearchState to console.debug. Returns a function that unsubscribes all listeners installed by this call. Import from the dedicated sub-path so it's tree-shaken from production bundles.

Development only

Logs the full, literal search query string — if your queries may carry PII (names, emails, medical/financial terms typed by end users), don't enable this in production.

Example

import { createIndex, createSearch } from '@vielzeug/scout';
import { debugSearch } from '@vielzeug/scout/devtools';

const index = createIndex([{ name: 'Ada Lovelace' }], { fields: ['name'] });
const search = createSearch(index);
const stopDebugging = debugSearch(search);

search.query.value = 'alice';
// [scout:search] query -> "alice"
// [scout:search] isSearching -> true
// [scout:search] isSearching -> false
// [scout:search] results -> 1 item(s)

stopDebugging();

Types

`SearchConstraints`

Shared search-tuning knobs used by ScoutIndexOptions, CreateSearchOptions, and all search functions.

type SearchConstraints = {
  limit?: number;           // finite non-negative integer; default 50
  minQueryLength?: number;  // finite positive integer; default 3
  threshold?: number;       // finite 0..1 value; default 0.2
};

`FieldDef<T>`

type FieldDef<T> =
  | (keyof T & string)
  | {
      field: keyof T & string;
      weight?: number;      // default 1
      stringify?: (value: unknown) => string;
    };

`ScoutIndexOptions<T>`

type ScoutIndexOptions<T> = SearchConstraints & {
  fields: ReadonlyArray<FieldDef<T>>;
};

`CreateSearchOptions`

type CreateSearchOptions = SearchConstraints & {
  debounce?: number;   // finite non-negative integer; default 200
};

`SearchResult<T>`

type SearchResult<T> = {
  item: T;
  matches: FieldMatch<keyof T & string>[];  // literal normalized-token ranges; may be empty for fuzzy-only results
  score: number;                            // [0, 1]; 1 when query is empty
};

`FieldMatch<F>`

Generic over the union of field names — match.field is typed to the actual fields of T.

type FieldMatch<F extends string = string> = {
  field: F;
  ranges: [number, number][];  // literal normalized-token [start, end] ranges in original field value
};

`HighlightPart`

type HighlightPart = {
  highlighted: boolean;
  text: string;
};

`SearchState<T>`

See createSearch() above.

`ReactiveSearch<T>`

type ReactiveSearch<T> = SearchState<T> & {
  readonly index: ScoutIndex<T>;
};

See createReactiveSearch() above.

Errors

`ScoutError`

Base class for all scout errors. Use instanceof ScoutError to catch any scout-originated error.

class ScoutError extends Error {}

Named subclasses

Class	Thrown when
`ScoutConfigurationError`	An index, search, or reactive search receives invalid fields or numeric options
`ScoutDisposedError`	A method is called on a disposed `SearchState` instance

API Overview ​

Package Entry Point ​

createIndex(items, options) ​

ScoutIndex<T> ​

.search(query, options?) ​

.add(item) ​

.remove(item) ​

.reindex(item) ​

.setItems(items) ​

.size ​

.items ​

.onMutate(listener) ​

.revision ​

createSearch(index, options?) ​

createReactiveSearch(items, options) ​

findMatchRanges(text, query) ​

highlight(text, ranges) ​

highlightField(result, field, text) ​

toSearchMatcher(index, options?) ​

toFilterPredicate(index, query, options?) ​

segmentWords(text) ​

debugSearch(search) ​

Types ​

SearchConstraints ​

FieldDef<T> ​

ScoutIndexOptions<T> ​

CreateSearchOptions ​

SearchResult<T> ​

FieldMatch<F> ​

HighlightPart ​

SearchState<T> ​

ReactiveSearch<T> ​

Errors ​

ScoutError ​

API Overview

Package Entry Point

`createIndex(items, options)`

`ScoutIndex<T>`

`.search(query, options?)`

`.add(item)`

`.remove(item)`

`.reindex(item)`

`.setItems(items)`

`.size`

`.items`

`.onMutate(listener)`

`.revision`

`createSearch(index, options?)`

`createReactiveSearch(items, options)`

`findMatchRanges(text, query)`

`highlight(text, ranges)`

`highlightField(result, field, text)`

`toSearchMatcher(index, options?)`

`toFilterPredicate(index, query, options?)`

`segmentWords(text)`

`debugSearch(search)`

Types

`SearchConstraints`

`FieldDef<T>`

`ScoutIndexOptions<T>`

`CreateSearchOptions`

`SearchResult<T>`

`FieldMatch<F>`

`HighlightPart`

`SearchState<T>`

`ReactiveSearch<T>`

Errors

`ScoutError`