Service Catalog - Troubleshooting the error "ReferenceError: guideNext is not defined"

Issue

Problem

In the Service Catalog Order Guide, the user receives the following error in the Google Chrome or Mozilla Firefox browser developer tools when they click the Next UI button: ReferenceError: guideNext is not defined

This happens when an instance is upgraded from Eureka (or earlier) to Fuji or later releases.

Symptoms

The following symptoms are seen on the Service Catalog when replicating the issue:

Order Guide not going to the Choose Options page after clicking Next
Order Guide showing the Next button instead of the Choose Options page
ReferenceError: guideNext is not defined shown in the Developer Tools on Google Chrome and Mozilla Firefox

Cause

The cause of the issue is with the UI page com.glideapp.servicecatalog_cat_item_guide_view being modified in Eureka, or a previous release.

When the instance is upgraded to Fuji, or later, release, this causes the code within the UI page above to be skipped during the upgrade to maintain the customization. However this causes the updated code to not be applied to the UI page and therefore causes the error to be thrown.

Resolution

Warning: The following change involves modifying the functionality of the Order Guide checkout process. Therefore as a caution, please ensure that the resolution is applied to a sub-production instance and ensure that testing is in progress before applying the change to a production instance.

To provide resolution to the problem, the UI page com.glideapp.servicecatalog_cat_item_guide_view needs to be reverted to Base System. To do this, please perform the following step :

On the ServiceNow instance, find the navigation filter, and select System UI > UI Pages
Search for the UI page name com.glideapp.servicecatalog_cat_item_guide_view
Open up the UI page com.glideapp.servicecatalog_cat_item_guide_view
Ensure that the Versions related list is shown. If not, right-click the header, select Configure > Related List, then select Versions and click Save.
On the Versions Related List, click the record where the source contains the upgraded instance version
On the Version record, select Related Links > Revert to this version
Click OK