How can I resolve the n8n 'Cannot assign to read only property …' error in my sub-workflow?

Below is some troubleshooting advice based on n8n’s documentation:

Understanding the Error

The error message

  “Cannot assign to read only property ‘name’ of object ‘Error: Referenced node is unexecuted’”

indicates that the custom code node is trying to use data from a node (in this case, the one you’re referring to as "Input") that hasn’t executed. In other words, the node you’re referencing isn’t running before your code runs, so the expected data isn’t available. This is why the system returns an immutable error object.

Steps to Troubleshoot and Fix

1. Verify Workflow Execution Order
   Confirm that the node expected to provide input data (your “Input” node) actually executes before your custom code node.

   • Run your sub-workflow up to the data-providing node to see if it produces the expected output.
   • If you’re calling the sub-workflow via an Execute Workflow node in the parent workflow, make sure the node is configured to wait for sub-workflow completion. This ensures that all nodes in the sub-workflow, including the one that should provide data, have executed.

2. Check Node References
   In your custom code, you’re using:

   JSCopied
   let items = $items("Input");
   let target_section_name = items[0].json.target_section_name;

   Verify that the node named “Input” is indeed producing output. If the node has a different name or if it’s not connected properly, revise the reference accordingly.

3. Use Execution Checks (Optional)
   For custom logic, you might want to ensure a node has executed before trying to use its data. For example:

   JSCopied
   if ($("Input").isExecuted) {
     // Proceed with your code logic
   } else {
     // Handle the case where the data node didn't execute
   }

   This lets you conditionally run code only if the referenced node has produced output, avoiding the error.

4. Confirm Sub-Workflow Configuration
   Since your setup uses the Execute Workflow node to call a sub-workflow:

   • Ensure the sub-workflow is error free.
   • Verify that you’re using the correct mode (e.g., using “Wait for Sub-Workflow Completion” if you require synchronous output).

5. Deep Copy Data if Required
   If the incoming data is frozen (read-only), and you need to modify it, consider creating a deep copy before filtering or modifying its properties:

   JSCopied
   let items = $items("Input");
   let target_section_name = items[0].json.target_section_name;
   
   for (const item of $input.all()) {
       // Creating a deep copy ensures the object is mutable.
       let newData = JSON.parse(JSON.stringify(item.json.data));
       newData = newData.filter(d =>
           d.name.trim().toLowerCase() === target_section_name.trim().toLowerCase()
       );
       item.json.data = newData;
   }
   
   return $input.all();

Final Note

Based on the documentation, the error occurs when a node that’s referenced in an expression or code hasn’t executed, meaning your data pipeline might be out of sync. By confirming the order of execution and ensuring that the Execute Workflow node (and its sub-workflow) is properly configured (including waiting for completion), you should be able to restore the expected behavior.

This should help you pinpoint why the sub-workflow stopped working and lead to a solution without needing external intervention.