ServiceNow Code and Beyond: Client-Side vs Server-Side Scripting in ServiceNow

Welcome to the first entry in our new blog series, “ServiceNow Code and Beyond.” This series will dive deep into advanced ServiceNow development concepts, offering practical insights, tips, and techniques to help you build more efficient and effective applications. In this post, we will explore the differences between client-side and server-side scripting in ServiceNow, their use cases, and best practices to help you decide which approach is right for your needs.

Understanding Client-Side vs. Server-Side Scripting

Before diving into the specifics, let’s clarify what we mean by client-side and server-side scripting in ServiceNow.

• Client-Side Scripting: This involves scripts that run in the user’s browser. In ServiceNow, common client-side scripting options include Client Scripts, UI Actions, and UI Policies. These scripts primarily handle tasks such as form validation, dynamic field manipulation, and user interaction enhancements.

• Server-Side Scripting: These scripts run on the ServiceNow server and include Business Rules, Script Includes, Scheduled Jobs, and Workflow Scripts. Server-side scripts handle data processing, logic implementation, and other back-end operations best executed on the server.

Now, let’s look at when and why you might use each type of scripting and the best practices to consider.

Performance and Optimization

One of the most critical factors in deciding between client-side and server-side scripting is performance.

• Client-Side Scripting for Faster User Experience: Client-side scripts execute in the user’s browser, which can make certain actions faster since they don’t require a round trip to the server. For example, validating a form field with a client script can provide immediate feedback to the user, enhancing their experience. However, overuse of client-side scripts can lead to performance issues, especially if they involve complex logic or frequent changes to the DOM (Document Object Model).

• Just-In-Time Training: Client-side logic is generally able to monitor the user’s input in real-time and knows exactly what is stored in the browser at any given moment. This makes client-side techniques nimble and dynamic, often able to give the user immediate feedback. For this reason, client-side logic is often used for “just-in-time” training, user experience improvements, and lightweight field validation or automation. However, these techniques only know data that’s in the browser; they don’t know related information stored on the server.

Example: Server-Side Script for Data Processing

This script provides real-time validation of user input, ensuring only letters are entered. It’s efficient, runs quickly, and improves the user experience by providing immediate feedback.

• Server-Side Scripting for Heavy Lifting: Server-side scripts are better suited for tasks that require processing large amounts of data or need access to backend resources. They can be optimized to run efficiently on the server,

reducing the workload on the client. For instance, a server-side Business Rule might calculate a complex discount for a large dataset, which would be inefficient to do on the client side.

Example: Server-Side Script for Data Processing

This server-side script efficiently calculates the total order price for a customer by querying the database, a task that would be too resource-intensive for client-side scripting.

Differences in Objects and Methods Between Client-Side and Server-Side Scripting

A critical difference between client-side and server-side scripting in ServiceNow is the availability of objects and methods. For example, the g_form object, which is used to manipulate form fields, is only available in client-side scripts. On the other hand, objects like GlideRecord are exclusive to the server side for database operations.

When writing scripts, always be mindful of the context in which your code is running. For instance, attempting to use g_form in a server-side script will result in an error because it is not defined on the server. Similarly, server-side objects such as gs (GlideSystem) and current (a GlideRecord object representing the current record) are not available in the client context.

Bridging Client-Side and Server-Side Scripting with AJAX

In scenarios where you need to bridge the gap between client-side and server-side scripting, AJAX (Asynchronous JavaScript and XML) can be a powerful tool. AJAX allows you to send and receive data asynchronously between the client and server without requiring a page reload, which is particularly useful for creating dynamic, responsive applications.

For example, in ServiceNow, you can use GlideAjax on the client side to call a server-side Script Include. This can fetch data from the server or perform actions without refreshing the entire page.

User Experience Considerations

• Client-Side Scripting for Enhanced Interactivity: Client-side scripts are essential for enhancing the user experience by providing dynamic and interactive features. For example, you can use Client Scripts to auto-populate fields, show or hide form sections, or update UI elements based on user actions.
•  Server-Side Scripting to Maintain Data Integrity: While client-side scripting can improve interactivity, server-side scripting is crucial for maintaining data integrity and ensuring that all business logic is consistently applied. Server-side scripts are not visible or accessible to users, making them ideal for critical operations that must be secure and tamper-proof.

Security Considerations

• Client-Side Security Risks: Because client-side scripts run in the user’s browser, they are more exposed to security risks such as Cross-Site Scripting (XSS) attacks. To mitigate these risks, ensure that all client-side scripts validate input and avoid exposing sensitive data.
• Server-Side Security Benefits: Server-side scripts, being executed on the server, are inherently more secure. They cannot be tampered with by users, making them ideal for sensitive operations such as authentication, authorization, and data validation. One valuable tool for enhancing security in server-side scripting is the GlideRecordSecure API. This API respects Access Control Lists (ACLs), ensuring that only authorized data is accessible and reducing the risk of unauthorized access.

Using Modern JavaScript Syntax (ES12 and Beyond)

ServiceNow supports modern JavaScript syntax, including ES12 (ECMAScript 2021). This allows you to use advanced language features like optional chaining (?.), nullish coalescing (??), and more, making your scripts more concise and maintainable.

For example, instead of writing:

You can use optional chaining to simplify the code:

If you’re working with the Xanadu release or later, ServiceNow provides full support for these modern JavaScript features, enabling you to write more efficient and expressive code.

Best Practices for Client-Side and Server-Side Scripting

1. Use Client-Side Scripts Sparingly: Avoid heavy client-side scripts that slow down the user’s browser or impact page load times. Use client-side scripts primarily for enhancing user interaction and providing immediate feedback.
2. Leverage Server-Side Scripts for Data Processing: For operations that involve complex calculations, data manipulation, or access to back-end resources, use server-side scripting. Ensure these scripts are optimized to minimize server load and response time.
3. Secure Your Scripts: Always validate inputs on both client and server sides. Never trust data from the client and always sanitize it on the server side to prevent XSS and other attacks. Utilize GlideRecordSecure for server-side data operations to ensure ACL compliance and enhanced security.
4. Optimize for Performance: Use caching and minimize database queries in server-side scripts. For client-side scripts, avoid excessive DOM manipulation and minimize the use of global variables.
5. Code Reusability: For both client and server-side scripts, strive for reusability. Use Script Includes for reusable server-side logic and consider creating reusable functions or modules for client-side code.

Visual Overview: When to Use Client-Side vs. Server-Side Scripting

Conclusion and Next Steps

Choosing between client-side and server-side scripting in ServiceNow depends on your specific use case, performance needs, and security considerations. By understanding the strengths and limitations of each, and leveraging tools like AJAX, you can make informed decisions to optimize your applications. Embracing modern JavaScript syntax and adhering to best practices will further enhance your scripts’ effectiveness and maintainability.

Try It Yourself!

We encourage you to try out the code samples provided and see how they impact your applications. Experiment with different approaches to find what works best for your specific requirements.

Stay tuned for the next blog post in the “ServiceNow Code and Beyond” series, where we’ll explore “Advanced Scripting Techniques in ServiceNow,” diving into writing efficient and reusable scripts using GlideRecord, GlideAggregate, and GlideRecordSecure.