fix: update SlackListsItemFieldMessage to support single and array message shapes

[swayamsingh2004]

Fixes #2598

Problem

SlackListsItemFieldMessage typed the message field as string[], which was incorrect in two ways:

1. The Slack API can return message as either a single object or an array of objects
2. The elements are message objects (with text, ts, etc.), not strings

Solution

• Added a new SlackListsItemMessage interface with optional fields: text, ts, user, team, type
• Changed message: string[] to message: SlackListsItemMessage | SlackListsItemMessage[] to handle both shapes the API can return

References

• Closes SlackListsItem FieldMessage.message type does not match API response shape #2598
• Same inconsistency reported on Java SDK: ListRecord.Field.message` deserialization fails when Slack returns an array java-slack-sdk#1587

[changeset-bot]

🦋 Changeset detected

Latest commit: 9df488e

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@slack/web-api	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[salesforce-cla]

Thanks for the contribution! Before we can merge this, we need @swayamsingh2004 to sign the Salesforce Inc. Contributor License Agreement.

[srtaalej]

hi @swayamsingh2004 thank you for taking the time to fix this issue! I will take a look at the code and make sure its all correct for merge 💟

[srtaalej]

LGTM and working well ⭐ ⭐ ⭐

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.88%. Comparing base (66e6cdb) to head (9df488e).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2627   +/-   ##
=======================================
  Coverage   88.88%   88.88%           
=======================================
  Files          62       62           
  Lines       10238    10238           
  Branches      451      451           
=======================================
  Hits         9100     9100           
  Misses       1117     1117           
  Partials       21       21           

Flag	Coverage Δ
cli-hooks	88.88% <ø> (ø)
cli-test	88.88% <ø> (ø)
logger	88.88% <ø> (ø)
oauth	88.88% <ø> (ø)
socket-mode	88.88% <ø> (ø)
web-api	88.88% <ø> (ø)
webhook	88.88% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[srtaalej]

Related issues across SDKs

This is the same underlying API inconsistency that was reported and fixed in the Java SDK:

• node-slack-sdk: SlackListsItem FieldMessage.message type does not match API response shape #2598 (the issue this PR fixes)
• java-slack-sdk: ListRecord.Field.message` deserialization fails when Slack returns an array java-slack-sdk#1587 — ListRecord.Field.message deserialization fails when Slack returns an array
• java-slack-sdk: fix(model): handle array format for ListRecord.Field message deserial… java-slack-sdk#1590 — the fix (merged May 2026)
• java-slack-sdk: Slack API issues with deserializing api payloads java-slack-sdk#1450 — earlier report of the same deserialization issue
• java-slack-sdk: JsonSyntaxException when deserializing message using conversation.history java-slack-sdk#1454 — duplicate closed in favor of Add isActive property to the SocketModeClient #1450