ServiceNow Errors: Understanding "Unhandled Exception in GlideAjax"

As a ServiceNow developer, you've likely encountered the need for client-side scripts to interact with server-side logic. GlideAjax is a powerful tool for this asynchronous communication, allowing your forms and portal widgets to dynamically fetch or update data without full page reloads. However, you might have stumbled upon a frustrating error message in your browser console: "Unhandled exception in GlideAjax." This cryptic message can halt your development progress. This article aims to demystify this common ServiceNow error, explore its root causes, and equip you with effective troubleshooting strategies to get your scripts back on track.

The "Unhandled exception in GlideAjax" error in ServiceNow signifies that something went wrong during the asynchronous communication between your client-side script and the server-side GlideAjax script include. Essentially, your client script sent a request to the server, but the server either failed to process it correctly or returned an unexpected response that the client script couldn't handle.

Common Culprits Behind the Error

Several factors can lead to this "Unhandled exception." Here are some of the most frequent causes:

• Incorrectly Referenced or Non-Existent Script Include: The client-side GlideAjax call specifies the name of a script include. If this name is misspelled, or if the script include doesn't actually exist in your ServiceNow instance, the server won't be able to find the requested resource, leading to an exception.

  
  

• Mismatched Function Names: Within the GlideAjax call, you use the addParam('sysparm_name', 'yourFunctionName') method to specify which function within the script include should be executed. If the value you provide for 'yourFunctionName' doesn't exactly match the name of a function in your script include, the server won't know which code to run.

  
  

• Script Include Not Marked as "Client Callable": For a script include to be accessible via GlideAjax from a client-side script, the "Client callable" checkbox on the script include record must be selected. If this box is unchecked, the server will refuse the connection, resulting in the unhandled exception.

  
  

• Errors Within the Server-Side Script Include: The code within your GlideAjax script include might contain syntax errors, logical flaws, or runtime exceptions. These errors can prevent the script from executing successfully and returning a valid response to the client.

  
  

• Unexpected Response Format: Your client-side script might be expecting the server to return data in a specific format (e.g., JSON), but the server-side script is returning something else or nothing at all. This mismatch can cause errors when the client script tries to process the response.

  
  

• Issues with Passed Parameters: The parameters you pass from your client-side script using ga.addParam() might not be correctly received or handled in your server-side script include. This could lead to errors during the server-side processing.

Troubleshooting Steps to Resolve the Error

When you encounter the "Unhandled exception in GlideAjax" error, follow these steps to diagnose and resolve the issue:

1. Verify the Script Include Name: Double-check the exact spelling and capitalization of the script include name you're using in your client-side GlideAjax call. Navigate to System Definition > Script Includes in ServiceNow and confirm that a script include with that name exists.

   
   

2. Confirm the Function Name: Ensure that the value you're passing as the sysparm_name parameter in your GlideAjax call precisely matches the name of the function you intend to execute within your script include. Pay attention to case sensitivity.

   
   

3. Check the "Client Callable" Setting: Open your GlideAjax script include in ServiceNow and verify that the "Client callable" checkbox is selected. If it's not, check it and save the record.

   
   

4. Examine Server-Side Script Logs: Add gs.log() statements within your GlideAjax script include to track its execution flow and identify any potential errors. After triggering the GlideAjax call, check the system logs (System Logs > System Log > All) for any logged messages or errors originating from your script include.

   
   

5. Inspect the Client-Side Response: In your client-side script's callback function (the function that handles the response from GlideAjax), add a console.log(response) statement. This will print the raw response received from the server to your browser's developer console. Examine this response to see if it's in the expected format and contains any error messages.

   
   

6. Validate Parameter Passing: Ensure that the parameters you're adding using ga.addParam() in your client-side script are being correctly retrieved in your server-side script include using this.getParameter('your_parameter_name'). Log the values of these parameters on the server-side to confirm they are being passed as expected.

   
   

7. Review Client-Side Script Logic: Carefully examine the part of your client-side script that processes the response from the GlideAjax call. Ensure that you're correctly parsing the data (if it's in JSON format, use JSON.parse()) and handling any potential errors.

   
   

8. Consider Returning JSON Objects: A robust approach for handling multiple values from a GlideAjax call is to return a JSON object from your script include. On the server-side, create an object, populate it with the data you want to send back, and then use JSON.stringify() to convert it into a string. In your client-side script's callback function, parse this string back into a JavaScript object using JSON.parse(). This makes it easier to access and work with the returned data.

   
   

   Example (Server-Side Script Include):

   JavaScript

   
   

Example (Client-Side Script):

JavaScript

Practical Examples

GlideAjax is commonly used in ServiceNow for various purposes, including:

• Dynamically populating dropdown fields based on user selections.

• Validating user input against server-side data.

• Fetching and displaying additional information related to a selected record.

• Triggering server-side workflows or processes based on client-side actions.

Alternative Solutions

While GlideAjax is often the go-to solution for asynchronous client-server communication, in some scenarios, you might consider alternative approaches like:

• UI Policies: For simple client-side logic and field manipulation without server interaction.

• Business Rules (with Client Callable checked): While technically server-side, business rules marked as client callable can sometimes achieve similar outcomes for data manipulation, though GlideAjax offers more flexibility for complex interactions.

However, for true asynchronous communication and fetching data from the server on demand, GlideAjax remains a fundamental and powerful tool in the ServiceNow developer's arsenal.

Conclusion

The "Unhandled exception in GlideAjax" error can be a stumbling block, but by understanding its common causes and following a systematic troubleshooting approach, you can effectively diagnose and resolve these issues. Remember to meticulously verify your script include names, function names, "Client callable" settings, and the data being exchanged between your client and server-side scripts. Leveraging logging and the browser's developer console are invaluable techniques for pinpointing the root of the problem. By mastering GlideAjax and its potential pitfalls, you'll be well-equipped to build dynamic and responsive ServiceNow applications. The next time you encounter this error, take a deep breath, systematically work through the troubleshooting steps outlined above, and you'll be well on your way to a solution.