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

Same type-check as Json.ts but in the JSONLines loader: each parsed record's pageContent must be a string. Fires when a JSONL pointer resolves to a non-string value (number, boolean, array, object, null) on any line.

Source

Thrown at packages/components/nodes/documentloaders/Jsonlines/Jsonlines.ts:263

        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

1. Inspect line i+1 of the .jsonl file — the pointed-to field is not a string.
2. Point the pointer at a guaranteed string field across all lines.
3. Normalize the JSONL upstream so every line's target field is a string.
4. Drop or transform non-conforming lines before loading.

Example fix

// before - pointer '/count' is numeric in some lines
new JSONLinesLoader(file, '/count')
// after - target the text field
new JSONLinesLoader(file, '/message')

// Validate every line of the JSONL resolves to a string at the pointer
function validateJsonlPointers(text, pointer) {
  const jp = require('jsonpointer')
  const lines = text.split(/\r?\n/).filter(Boolean)
  lines.forEach((line, i) => {
    const rec = JSON.parse(line)
    const v = pointer ? jp.get(rec, pointer) : rec
    if (typeof v !== 'string') throw new Error(`line ${i + 1}: pointer '${pointer}' is ${typeof v}, not string`)
  })
}

function isStringRecord(value) { return typeof value === 'string' }

try {
  return await jsonLinesLoader.load()
} catch (e) {
  if (/Expected string, at position/.test(e.message)) {
    throw new Error('JSONL target field is not a string on some line — check pointer', { cause: e })
  }
  throw e
}

When it happens

Trigger: A JSONL pointer like '/value' resolves to a number on some line; the pointer is omitted so each parsed line (an object) becomes pageContent; a malformed JSONL line parses to null.

Common situations: Streaming logs where the 'message' field is sometimes a string and sometimes an object; pointing at a numeric metric field; mixed-schema JSONL exports.

Related errors

• Expected string, at position ${i} got ${typeof pageContent}
• Invalid JSON in the Chat NVIDIA NIM's baseOptions: ${excepti
• Invalid JSON in the ChatOpenAI's BaseOptions: ${exception}
• Invalid JSON in the ChatOpenAI's BaseOptions: ${exception}
• Invalid JSON in the ChatOpenRouter's BaseOptions: ${exceptio

AI-assisted analysis of FlowiseAI/Flowise@abe4a8601a (2026-08-12). Data as JSON: /api/errors/d907f6131d332a41. Report an issue: GitHub.