deepseek-ai/deepseek-harness · error · MaterializeError

arrays with non-index properties are not JSON data

Error message

arrays with non-index properties are not JSON data

What it means

Error "arrays with non-index properties are not JSON data" thrown in deepseek-ai/deepseek-harness.

Source

Thrown at packages/workflow/workflow-worker-thread/src/realm.ts:121

    if (Array.isArray(objectValue)) return materializeArray(objectValue, path, seen)
    return materializeObject(objectValue, path, seen)
  } finally {
    seen.delete(objectValue)
  }
}

function materializeArray(value: unknown[], path: string, seen: Set<object>): unknown[] {
  const out: unknown[] = []
  for (let index = 0; index < value.length; index++) {
    if (!(index in value)) throw new MaterializeError(`${path}[${index}]`, 'sparse arrays are not JSON data')
    out.push(materialize(value[index], `${path}[${index}]`, seen))
  }
  // Own enumerable props beyond the indices (e.g. `arr.total = 3`) would be
  // silently dropped by JSON — reject them instead.
  for (const key of Object.keys(value)) {
    const index = Number(key)
    if (!Number.isInteger(index) || index < 0 || index >= value.length) {
      throw new MaterializeError(`${path}.${key}`, 'arrays with non-index properties are not JSON data')
    }
  }
  if (Object.getOwnPropertySymbols(value).length > 0) {
    throw new MaterializeError(path, 'symbol-keyed properties are not plain JSON data')
  }
  return out
}

function materializeObject(value: object, path: string, seen: Set<object>): Record<string, unknown> {
  if (!hasPlainPrototype(value)) {
    throw new MaterializeError(path, 'only plain objects and arrays are JSON data (exotic prototype)')
  }
  if (Object.getOwnPropertySymbols(value).length > 0) {
    throw new MaterializeError(path, 'symbol-keyed properties are not plain JSON data')
  }
  const out: Record<string, unknown> = {}
  // Object.keys = own enumerable string keys, matching JSON.stringify's
  // property selection exactly (non-enumerable props never reach JSON output).

View on GitHub (pinned to b150a551b8)

Solutions

1. Move non-index properties off arrays into a separate object field before returning the value.

When it happens

Trigger: Thrown at packages/workflow/workflow-worker-thread/src/realm.ts:121 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of deepseek-ai/deepseek-harness@b150a551b8 (2026-08-24). Data as JSON: /api/errors/af3f2adda8a876e3. Report an issue: GitHub.