fix(core): Resolve $().item expressions in partial executions

[r00gm]

Summary

When using $('NodeName').item in the expression editor after a partial execution, the expression would fail with "Can't get data for expression" even though the referenced node had been executed successfully.

Root cause: .item uses paired item resolution which requires connectionInputData (the active node's input) to trace items back through the chain. In a partial execution where the active node hasn't run, connectionInputData is empty — even though the referenced node's data is available in runData.

Fix: When connectionInputData is empty and no pinned data exists, fall back to reading directly from the referenced node's runData. This matches what first()/last()/all() already do. The fallback only activates in the UI preview path — during real execution, connectionInputData is always populated before expressions are evaluated.

Related Linear tickets, Github issues, and Community forum posts

https://linear.app/n8n/issue/CAT-2396

Review / Merge checklist

• PR title and summary are descriptive. (conventions)
• Docs updated or follow-up ticket created.
• Tests included.

[codecov]

Bundle Report

Changes will increase total bundle size by 399 bytes (0.0%) ⬆️. This is within the configured threshold ✅

Detailed changes

Bundle name	Size	Change
editor-ui-esm	42.88MB	399 bytes (0.0%) ⬆️

Affected Assets, Files, and Routes:

view changes for bundle: editor-ui-esm

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
assets/constants-*.js	399 bytes	2.9MB	0.01%

[codspeed]

Merging this PR will not alter performance

✅ 32 untouched benchmarks
⏩ 7 skipped benchmarks¹

---

_{Comparing cat-2396-cant-see-node-output-in-expressions-if-there-are-un-executed (9662b28) with master (24dcf75)}

Footnotes

1. 7 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[codecov]

Codecov Report

❌ Patch coverage is 58.33333% with 5 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
packages/workflow/src/workflow-data-proxy.ts	58.33%	5 Missing ⚠️

📢 Thoughts on this report? Let us know!

[cubic-dev-ai]

1 issue found across 2 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="packages/workflow/src/workflow-data-proxy.ts">

<violation number="1" location="packages/workflow/src/workflow-data-proxy.ts:1242">
P2: The new `.item` fallback validates only `itemIndex >= length`; negative indexes can still pass and cause an undefined access in `returnExecutionData`.</violation>
</file>

Architecture diagram

sequenceDiagram
    participant UI as "Expression Editor (UI)"
    participant Proxy as "WorkflowDataProxy"
    participant State as "Execution State (runData)"
    participant Input as "Active Node Input (connectionInputData)"

    Note over UI,Input: Scenario: Partial Execution (Active node has not run yet)

    UI->>Proxy: "Resolve $('NodeName').item"
    Proxy->>Proxy: "Check for Pinned Data"

    alt No Pinned Data found
        Proxy->>Input: "Request paired item data"
        Input-->>Proxy: "[Empty] (Node hasn't executed)"

        alt NEW: UI Preview Fallback (connectionInputData is empty)
            Proxy->>State: "getNodeExecutionOrPinnedData('NodeName')"
            State-->>Proxy: "Return available items from previous runs"

            alt Node has execution data
                Proxy->>Proxy: "NEW: Resolve item by itemIndex (default 0)"
            else Node has no data
                Proxy-->>UI: "Throw Can't get data for expression"
            end
        else Standard Execution Path
            Proxy->>Input: "Map item via pairedItem index"
            Input-->>Proxy: "Return mapped item"
        end
    end

    Proxy-->>UI: "Return JSON data for Preview"

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_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

[cubic-dev-ai]

P2: The new .item fallback validates only itemIndex >= length; negative indexes can still pass and cause an undefined access in returnExecutionData.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At packages/workflow/src/workflow-data-proxy.ts, line 1242:

<comment>The new `.item` fallback validates only `itemIndex >= length`; negative indexes can still pass and cause an undefined access in `returnExecutionData`.</comment>

<file context>
@@ -1229,6 +1229,24 @@ export class WorkflowDataProxy {
+										if (nodeRunData.length) {
+											// In the UI preview itemIndex is always 0, but guard against
+											// out-of-bounds access in case that assumption ever changes.
+											if (itemIndex >= nodeRunData.length) {
+												throw createExpressionError(
+													`"${nodeName}" node has ${nodeRunData.length} item(s) but expression references item ${itemIndex}`,
</file context>

Suggested change

	if (itemIndex >= nodeRunData.length) {
	if (itemIndex < 0 || itemIndex >= nodeRunData.length) {

[n8n-assistant]

Got released with n8n@2.15.0