UI Page not loading: page script error on load

JavaScript syntax errors or runtime exceptions in the UI Page's client script section, such as undefined variables, missing functions, or improper API calls. (high likelihood)

Server-side Jelly template syntax errors including malformed XML tags, incorrect GlideRecord queries, or invalid server-side script blocks. (high likelihood)

Missing or invalid dependencies such as referenced CSS files, JavaScript libraries, or other UI Pages that the current page depends on. (medium likelihood)

Access control restrictions preventing the user from viewing required records or tables referenced in the UI Page scripts. (medium likelihood)

Database connection issues or query timeouts when the UI Page attempts to load data during initialization. (low likelihood)

Step 1: Open the browser developer tools (F12) and check the Console tab for JavaScript errors while loading the UI Page. Note any specific error messages, line numbers, and function names.

Step 2: Navigate to System Diagnostics > Log > Application Log in ServiceNow and filter by the current timestamp to identify server-side errors related to the UI Page loading.

Step 3: Access the problematic UI Page record at System UI > UI Pages and review the HTML template and client script sections for syntax errors, undefined variables, or malformed code.

Step 4: Test the UI Page in isolation by navigating directly to it using the URL format: https://instance.service-now.com/nav_to.do?uri=/$ui-page-name.do to isolate the error from portal or frame contexts.

Step 5: Validate all GlideRecord queries and server-side scripts in the Jelly template by testing them in a background script at System Definition > Scripts > Background Scripts.

Step 6: Check that all referenced CSS stylesheets, JavaScript libraries, and dependent UI Pages exist and are accessible by reviewing the HTML head section and any g:requires tags.

Step 7: Verify user permissions by testing the UI Page with an admin account and checking ACL rules on any tables or records accessed by the page scripts.

Step 8: If errors persist, create a simplified version of the UI Page with minimal code to identify which specific section is causing the failure, then gradually add functionality back.