krisk/Fuse · error · Error

Incorrect 'index' type

Error message

Incorrect 'index' type

What it means

Fuse.setCollection(docs, index) accepts an optional pre-built index as its second argument, but it must be a genuine FuseIndex instance. Passing anything else (plain object, array, index from a different Fuse copy) throws this error so a malformed index is never silently used. It exists to catch stale or hand-rolled index objects.

Source

Thrown at src/core/index.ts:112

  _getSearcher(query: string): Searcher {
    if (this._lastQuery === query) {
      return this._lastSearcher!
    }
    const opts = this._invertedIndex
      ? { ...this.options, _invertedIndex: this._invertedIndex }
      : this.options
    const searcher = createSearcher(query, opts)
    this._lastQuery = query
    this._lastSearcher = searcher
    return searcher
  }

  setCollection(docs: ReadonlyArray<T>, index?: FuseIndex<T>): void {
    this._docs = docs as T[]

    if (index && !(index instanceof FuseIndex)) {
      throw new Error(ErrorMsg.INCORRECT_INDEX_TYPE)
    }

    this._myIndex =
      index ||
      createIndex(this.options.keys, this._docs, {
        getFn: this.options.getFn,
        fieldNormWeight: this.options.fieldNormWeight
      })

    if (this.options.useTokenSearch) {
      const analyzer = createAnalyzer({
        isCaseSensitive: this.options.isCaseSensitive,
        ignoreDiacritics: this.options.ignoreDiacritics,
        tokenize: this.options.tokenize
      })
      this._invertedIndex = buildInvertedIndex(
        this._myIndex.records,
        this._myIndex.keys.length,

View on GitHub (pinned to edf2fb608e)

Solutions

1. Create the index with Fuse.createIndex(keys, docs) from the SAME installed Fuse module and pass that to setCollection.
2. Omit the second argument and let Fuse build the index itself.
3. Dedupe fuse.js in node_modules if instanceof mismatches come from multiple package copies.

Example fix

// before
const index = buildMyOwnIndex(keys, docs) // plain object
fuse.setCollection(newDocs, index)
// after
import Fuse from 'fuse.js'
const index = Fuse.createIndex(['title'], newDocs)
fuse.setCollection(newDocs, index)

import Fuse, { FuseIndex } from 'fuse.js'
if (index !== undefined && !(index instanceof FuseIndex)) {
  throw new TypeError('setCollection requires a FuseIndex from Fuse.createIndex')
}
fuse.setCollection(docs, index)

const isFuseIndex = (v) => v instanceof FuseIndex

try {
  fuse.setCollection(docs, index)
} catch (e) {
  if (e.message === "Incorrect 'index' type") {
    fuse.setCollection(docs) // let Fuse rebuild the index
  } else {
    throw e
  }
}

When it happens

Trigger: fuse.setCollection(docs, someObject) where someObject is not created by Fuse.createIndex(...) — e.g. a serialized/cached index from a different Fuse version, a plain array, or a duplicate-package instanceof mismatch.

Common situations: Caching indexes built by a different installed copy of fuse.js (duplicate dependency causing instanceof to fail); hand-rolling an index object; upgrading Fuse while reusing old serialized indexes.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• Invalid doc index: must be a non-negative integer within the

AI-assisted analysis of krisk/Fuse@edf2fb608e (2026-09-02). Data as JSON: /api/errors/e831b5384e834995. Report an issue: GitHub.