What causes "Return output must be an object" in FlowiseAI/Flowise?

Ensure every code path returns an object literal, e.g. return { result: value }.

FlowiseAI/Flowise · error · Error

Return output must be an object

Error message

Return output must be an object

What it means

The 'Update State Memory (Code)' tab runs sandboxed JS whose return value is merged into agent state; it must be an object so its keys become state properties. A non-object return (string, number, boolean, undefined) throws. The executed code and the type check both live inside the try block, so a thrown JS error is also re-wrapped by the catch.

Source

Thrown at packages/components/nodes/sequentialagents/LLMNode/LLMNode.ts:719

                let value = sch.value as string
                if (value.startsWith('$flow')) {
                    value = customGet(flow, sch.value.replace('$flow.', ''))
                } else if (value.startsWith('$vars')) {
                    value = customGet(flow, sch.value.replace('$', ''))
                }
                obj[key] = value
            }
            return obj
        } catch (e) {
            throw new Error(e)
        }
    } else if (selectedTab === 'updateStateMemoryCode' && updateStateMemoryCode) {
        const sandbox = createCodeExecutionSandbox(input, variables, flow)

        try {
            const response = await executeJavaScriptCode(updateStateMemoryCode, sandbox)

            if (typeof response !== 'object') throw new Error('Return output must be an object')
            return response
        } catch (e) {
            throw new Error(e)
        }
    }
}

module.exports = { nodeClass: LLMNode_SeqAgents }

View on GitHub (pinned to abe4a8601a)

Solutions

Ensure every code path returns an object literal, e.g. return { result: value }.
If producing a single scalar, wrap it: return { score: n }.
If returning a JSON string, parse it first: return JSON.parse(str).

Example fix

// before (throws: returns a string)
return JSON.stringify({ topic: input })

// after
return { topic: input }

Defensive patterns

Strategy: type-guard

Validate before calling

const response = await executeJavaScriptCode(updateStateMemoryCode, sandbox)
if (response === null || typeof response !== 'object' || Array.isArray(response)) {
  throw new Error('Update State Memory code must return a plain object')
}

Type guard

const isPlainObject = (x: any): x is Record<string, unknown> =>
  typeof x === 'object' && x !== null && !Array.isArray(x)

Prevention

Always return an object literal from the code snippet.
If computing a scalar, wrap it: return { result: value }.
Never return JSON.stringify(...) — return the parsed object.

When it happens

Trigger: updateStateMemoryCode returns a primitive (e.g. a computed number or string), returns undefined (missing/empty return), or returns a JSON string instead of a parsed object.

Common situations: Code returns JSON.stringify(obj) instead of obj; a code path ends without a return; the snippet was written to print/log rather than return.

Related errors

AI-assisted analysis of FlowiseAI/Flowise@abe4a8601a (2026-08-12). Data as JSON: /api/errors/1a9358063e420e6b. Report an issue: GitHub.