- A
Convert the onChange script to a UI Policy with a condition on category and a script action to perform the query.
Why wrong: Wrong: UI Policy scripts still run client-side and would have the same synchronous blocking issue.
- B
Use a calculated field on the subcategory field that derives its value from a database view.
Why wrong: Wrong: Calculated fields are for simple expressions, not for populating choice lists or running GlideRecord queries.
- C
Replace the client script with a Scripted REST API that returns subcategory options, and make an asynchronous AJAX call from the client script to populate the field.
Correct: async AJAX avoids blocking the UI; server handles the heavy query.
- D
Move the query to a Business Rule that runs on 'before' and updates the subcategory field using setValue.
Why wrong: Wrong: Business Rule runs server-side but cannot directly update a client-side choice list; would require additional client mechanism.
Quick Answer
The correct answer is to replace the client script with a Scripted REST API that returns subcategory options, and make an asynchronous AJAX call from the client script to populate the field. This approach resolves the form freeze by offloading the large GlideRecord query on the cmdb_ci table from the client-side onChange script to the server, where it can process efficiently without blocking the UI thread. The asynchronous AJAX call, typically implemented via GlideAjax, ensures the form remains responsive while the subcategory options load in the background, maintaining real-time updates without the 10-15 second delay. On the ServiceNow Certified Application Developer CAD exam, this question tests your understanding of client-server architecture and performance optimization—specifically, that heavy database operations must never run synchronously in client scripts. A common trap is assuming a GlideAggregate or indexed fields alone will fix the freeze, but the core issue is synchronous blocking, not query speed. Memory tip: “Sync freezes, async pleases—keep heavy queries on the server side.”
SNOW-CAD User Interface Development Practice Question
This SNOW-CAD practice question tests your understanding of user interface development. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A ServiceNow developer is tasked with improving the performance of a custom incident form in the classic UI. The form includes a 'category' field that, when changed, triggers an onChange client script. This script uses a GlideRecord query to fetch related data from a large 'cmdb_ci' table (over 100,000 records) and populates a dependent field called 'subcategory' with relevant options. Users report that after selecting a category, the form freezes for 10-15 seconds before the subcategory field updates. The developer needs to maintain real-time updates based on the category selection. What is the best approach to resolve this performance issue while keeping the functionality?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"best"Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Replace the client script with a Scripted REST API that returns subcategory options, and make an asynchronous AJAX call from the client script to populate the field.
Option C is correct because it offloads the heavy GlideRecord query from the client to the server via a Scripted REST API, while using an asynchronous AJAX call (e.g., GlideAjax) to avoid blocking the UI thread. This eliminates the 10-15 second freeze by preventing synchronous server-side processing on the client, maintaining real-time updates without freezing the form.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Convert the onChange script to a UI Policy with a condition on category and a script action to perform the query.
Why it's wrong here
Wrong: UI Policy scripts still run client-side and would have the same synchronous blocking issue.
- ✗
Use a calculated field on the subcategory field that derives its value from a database view.
Why it's wrong here
Wrong: Calculated fields are for simple expressions, not for populating choice lists or running GlideRecord queries.
- ✓
Replace the client script with a Scripted REST API that returns subcategory options, and make an asynchronous AJAX call from the client script to populate the field.
Why this is correct
Correct: async AJAX avoids blocking the UI; server handles the heavy query.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Move the query to a Business Rule that runs on 'before' and updates the subcategory field using setValue.
Why it's wrong here
Wrong: Business Rule runs server-side but cannot directly update a client-side choice list; would require additional client mechanism.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often choose UI Policy (Option A) thinking it can run server-side logic, but UI Policies are purely client-side and cannot execute GlideRecord queries, leading to a misunderstanding of their scope.
Detailed technical explanation
How to think about this question
The key is using GlideAjax (or a Scripted REST API) to make an asynchronous call from the client script to a server-side script include or API endpoint. This allows the GlideRecord query to execute on the server without blocking the browser's JavaScript event loop, while the client script populates the subcategory field via a callback. In real-world scenarios with large tables like cmdb_ci, indexing the queried columns (e.g., category) can further reduce server response time, but the primary fix is avoiding synchronous client-server communication.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
- →
User Interface Development — study guide chapter
Learn the concepts, then practise the questions
- →
User Interface Development practice questions
Targeted practice on this topic area only
- →
All SNOW-CAD questions
500 questions across all exam domains
- →
ServiceNow Certified Application Developer CAD study guide
Full concept coverage aligned to exam objectives
- →
SNOW-CAD practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Related SNOW-CAD practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Working with Data practice questions
Practise SNOW-CAD questions linked to Working with Data.
Platform Features and Integration practice questions
Practise SNOW-CAD questions linked to Platform Features and Integration.
Integrating and managing application data practice questions
Practise SNOW-CAD questions linked to Integrating and managing application data.
Automating application logic with business rules and scripts practice questions
Practise SNOW-CAD questions linked to Automating application logic with business rules and scripts.
Application development using ServiceNow Studio practice questions
Practise SNOW-CAD questions linked to Application development using ServiceNow Studio.
Creating and customizing tables and data practice questions
Practise SNOW-CAD questions linked to Creating and customizing tables and data.
Designing interfaces and user experiences practice questions
Practise SNOW-CAD questions linked to Designing interfaces and user experiences.
Core Application Development practice questions
Practise SNOW-CAD questions linked to Core Application Development.
User Interface Development practice questions
Practise SNOW-CAD questions linked to User Interface Development.
SNOW-CAD fundamentals practice questions
Practise SNOW-CAD questions linked to SNOW-CAD fundamentals.
SNOW-CAD scenario practice questions
Practise SNOW-CAD questions linked to SNOW-CAD scenario.
SNOW-CAD troubleshooting practice questions
Practise SNOW-CAD questions linked to SNOW-CAD troubleshooting.
Practice this exam
Start a free SNOW-CAD practice session
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Questions learners often ask
What does this SNOW-CAD question test?
User Interface Development — This question tests User Interface Development — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Replace the client script with a Scripted REST API that returns subcategory options, and make an asynchronous AJAX call from the client script to populate the field. — Option C is correct because it offloads the heavy GlideRecord query from the client to the server via a Scripted REST API, while using an asynchronous AJAX call (e.g., GlideAjax) to avoid blocking the UI thread. This eliminates the 10-15 second freeze by preventing synchronous server-side processing on the client, maintaining real-time updates without freezing the form.
What should I do if I get this SNOW-CAD question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Keep practising
More SNOW-CAD practice questions
- A company has a custom table 'u_training_course' with a reference field to 'sys_user' named 'u_instructor'. The requirem…
- A company has a custom table 'u_asset' with a reference field 'u_location' pointing to 'cmn_location'. When a user chang…
- A developer needs to create a new application scope. Which of the following is a best practice when defining the scope?
- An application has a custom table 'u_project' with a field 'u_status' (choice list: Not Started, In Progress, Completed)…
- A company has a custom table 'u_incident_task' that extends 'task'. The developer wants to add a field 'u_approval' that…
- Which TWO of the following are types of UI Policies? (Choose two.)
Last reviewed: Jun 25, 2026
This SNOW-CAD practice question is part of Courseiva's free ServiceNow certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SNOW-CAD exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.