What causes "Expected string, at position ${i} got ${typeof pageContent}" in FlowiseAI/Flowise?

Inspect the JSON at the failing index i — the field the pointer targets is not a string.

FlowiseAI/Flowise · error · Error

Expected string, at position ${i} got ${typeof pageContent}

Error message

Expected string, at position ${i} got ${typeof pageContent}

What it means

Thrown by JSONTextLoader.load (Json.ts) during a type check on each parsed document: the loader expects every parsed pageContent to be a string. It fires when the JSON pointer resolves a field whose value is a number, boolean, array, object, or null rather than text.

Source

Thrown at packages/components/nodes/documentloaders/Json/Json.ts:286

        return [{ pageContent: raw, metadata: {} }]
    }

    public async load(): Promise<Document[]> {
        let text: string
        let metadata: Record<string, string>
        if (typeof this.filePathOrBlob === 'string') {
            const { readFile } = await TextLoader.imports()
            text = await readFile(this.filePathOrBlob, 'utf8')
            metadata = { source: this.filePathOrBlob }
        } else {
            text = await this.filePathOrBlob.text()
            metadata = { source: 'blob', blobType: this.filePathOrBlob.type }
        }
        const parsed = await this.parse(text)
        parsed.forEach((parsedData, i) => {
            const { pageContent } = parsedData
            if (typeof pageContent !== 'string') {
                throw new Error(`Expected string, at position ${i} got ${typeof pageContent}`)
            }
        })
        return parsed.map((parsedData, i) => {
            const { pageContent, metadata: additionalMetadata } = parsedData
            return new Document({
                pageContent,
                metadata:
                    parsed.length === 1
                        ? { ...metadata, ...additionalMetadata }
                        : {
                              ...metadata,
                              line: i + 1,
                              ...additionalMetadata
                          }
            })
        })
    }

View on GitHub (pinned to abe4a8601a)

Solutions

Inspect the JSON at the failing index i — the field the pointer targets is not a string.
Point the pointer at a string-valued field (e.g. '/body' or '/description') instead of '/id' or '/count'.
If you want non-string scalars as text, coerce them in a pre-processing step or pick a pointer to a string field.
If records are heterogeneous, filter or normalize the JSON before loading.

Example fix

// before: pointer '/price' resolves to a number
new JSONLoader(file, '/price')
// after: point at a text field, or stringify scalars
new JSONLoader(file, '/description')
// or coerce in the source data:
// data.forEach(r => { r.text = String(r.price) })

Defensive patterns

Strategy: type-guard

Validate before calling

// Walk the JSON at the pointer and ensure every resolution is a string
function pointerValuesAreStrings(json, pointer) {
  const records = Array.isArray(json) ? json : [json]
  return records.every((rec, i) => {
    const v = pointer ? require('jsonpointer').get(rec, pointer) : rec.text
    return typeof v === 'string'
  })
}

Type guard

function isStringPageContent(parsed) {
  return parsed.every((p, i) => typeof p.pageContent === 'string')
}

Try / catch

try {
  return await jsonLoader.load()
} catch (e) {
  if (/Expected string, at position (\d+) got (\w+)/.test(e.message)) {
    const [, idx, type] = e.message.match(/position (\d+) got (\w+)/)
    throw new Error(`JSON field at record ${idx} is ${type}, not a string — fix the pointer`, { cause: e })
  }
  throw e
}

Prevention

Point the JSON pointer at a guaranteed string field.
Pre-scan the JSON to confirm the target field is always a string.
Normalize non-string scalars to strings upstream.
For mixed schemas, filter or coerce records before loading.

When it happens

Trigger: A JSON pointer like '/price' resolves to a numeric field; '/tags' resolves to an array; the pointer is empty so the whole record becomes pageContent (an object); the source JSON has null where a string was expected.

Common situations: User points the loader at a numeric/boolean JSON field by mistake; a JSONL feed mixes schemas where some records have a string 'text' and others have an object; the pointer is omitted for a JSON array of non-string scalars.

Related errors

AI-assisted analysis of FlowiseAI/Flowise@abe4a8601a (2026-08-12). Data as JSON: /api/errors/bf3047b0cc4b0ff2. Report an issue: GitHub.