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Client-Side Components/Client Scripts/Dynamic Field Dependencies with GlideAjax/README.md

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+# Dynamic Field Dependencies with GlideAjax
+
+This folder contains advanced Client Script examples demonstrating real-time field dependencies using GlideAjax for server-side data retrieval, cascading dropdowns, and dynamic form behavior.
+
+## Overview
+
+Modern ServiceNow forms often require dynamic behavior based on user selections. This example demonstrates:
+- **Real-time field updates** using GlideAjax for server-side queries
+- **Cascading dropdown menus** that filter based on parent selections
+- **Conditional field visibility** based on complex business logic
+- **Debouncing** to prevent excessive server calls
+- **Loading indicators** for better user experience
+- **Error handling** for failed AJAX calls
+- **Performance optimization** with caching and batching
+
+## Script Descriptions
+
+- **dynamic_category_subcategory.js**: Client Script implementing cascading category/subcategory dropdowns with real-time filtering.
+- **conditional_field_loader.js**: Advanced example showing conditional field loading based on multiple dependencies.
+- **ajax_script_include.js**: Server-side Script Include (Client Callable) that provides data for the client scripts.
+- **debounced_field_validator.js**: Real-time field validation with debouncing to reduce server load.
+
+## Key Features
+
+### 1. GlideAjax Communication
+Efficient client-server communication:
+```javascript
+var ga = new GlideAjax('MyScriptInclude');
+ga.addParam('sysparm_name', 'getSubcategories');
+ga.addParam('sysparm_category', categoryValue);
+ga.getXMLAnswer(callback);
+```
+
+### 2. Cascading Dropdowns
+Dynamic filtering of child fields:
+- Parent field change triggers child field update
+- Child options filtered based on parent selection
+- Multiple levels of cascading supported
+- Maintains previously selected values when possible
+
+### 3. Debouncing
+Prevents excessive server calls:
+- Waits for user to stop typing before making request
+- Configurable delay (typically 300-500ms)
+- Cancels pending requests when new input received
+- Improves performance and user experience
+
+### 4. Loading Indicators
+Visual feedback during AJAX calls:
+- Shows loading spinner or message
+- Disables fields during data fetch
+- Clears loading state on completion or error
+- Prevents duplicate submissions
+
+## Use Cases
+
+- **Category/Subcategory Selection**: Filter subcategories based on selected category
+- **Location-Based Fields**: Update city/state/country fields dynamically
+- **Product Configuration**: Show/hide fields based on product type
+- **Assignment Rules**: Dynamically populate assignment groups based on category
+- **Cost Estimation**: Calculate and display costs based on selections
+- **Availability Checking**: Real-time validation of resource availability
+- **Dynamic Pricing**: Update pricing fields based on quantity/options
+
+## Implementation Requirements
+
+### Client Script Configuration
+- **Type**: onChange (for field changes) or onLoad (for initial setup)
+- **Table**: Target table (e.g., incident, sc_req_item)
+- **Field**: Trigger field (e.g., category)
+- **Active**: true
+- **Global**: false (table-specific for better performance)
+
+### Script Include Configuration
+- **Name**: Descriptive name (e.g., CategoryAjaxUtils)
+- **Client callable**: true (REQUIRED for GlideAjax)
+- **Active**: true
+- **Access**: public or specific roles
+
+### Required Fields
+Ensure dependent fields exist on the form:
+- Add fields to form layout
+- Configure field properties (mandatory, read-only, etc.)
+- Set up choice lists for dropdown fields
+
+## Performance Considerations
+
+### Optimization Techniques
+1. **Cache responses**: Store frequently accessed data client-side
+2. **Batch requests**: Combine multiple queries into single AJAX call
+3. **Minimize payload**: Return only required fields
+4. **Use indexed queries**: Ensure server-side queries use indexed fields
+5. **Debounce input**: Wait for user to finish typing
+6. **Lazy loading**: Load data only when needed
+
+### Best Practices
+- Keep Script Includes focused and single-purpose
+- Validate input parameters server-side
+- Handle errors gracefully with user-friendly messages
+- Test with large datasets to ensure performance
+- Use browser developer tools to monitor network calls
+- Implement timeout handling for slow connections
+
+## Security Considerations
+
+### Input Validation
+Always validate parameters server-side:
+```javascript
+// BAD: No validation
+var category = this.getParameter('sysparm_category');
+var gr = new GlideRecord('cmdb_ci_category');
+gr.addQuery('parent', category); // SQL injection risk
+
+// GOOD: Validate and sanitize
+var category = this.getParameter('sysparm_category');
+if (!category || !this._isValidSysId(category)) {
+    return '[]';
+}
+```
+
+### Access Control
+- Respect ACLs in Script Includes
+- Use GlideRecordSecure when appropriate
+- Don't expose sensitive data to client
+- Implement role-based filtering
+
+### XSS Prevention
+- Sanitize data before displaying
+- Use g_form.setValue() instead of innerHTML
+- Validate choice list values
+- Escape special characters
+
+## Error Handling
+
+### Client-Side
+```javascript
+ga.getXMLAnswer(function(response) {
+    if (!response || response === 'error') {
+        g_form.addErrorMessage('Failed to load data. Please try again.');
+        return;
+    }
+    // Process response
+});
+```
+
+### Server-Side
+```javascript
+try {
+    // Query logic
+} catch (ex) {
+    gs.error('Error in getSubcategories: ' + ex.message);
+    return 'error';
+}
+```
+
+## Testing Checklist
+
+- [ ] Test with empty/null values
+- [ ] Test with invalid input
+- [ ] Test with large datasets (1000+ records)
+- [ ] Test on slow network connections
+- [ ] Test concurrent user interactions
+- [ ] Test browser compatibility (Chrome, Firefox, Safari, Edge)
+- [ ] Test mobile responsiveness
+- [ ] Verify ACL enforcement
+- [ ] Check for console errors
+- [ ] Monitor network tab for performance
+
+## Browser Compatibility
+
+Tested and compatible with:
+- Chrome 90+
+- Firefox 88+
+- Safari 14+
+- Edge 90+
+- ServiceNow Mobile App
+
+## Related APIs
+
+- **GlideAjax**: Client-server communication
+- **GlideForm (g_form)**: Form manipulation
+- **GlideUser (g_user)**: User context
+- **GlideRecord**: Server-side queries
+- **JSON**: Data serialization
+
+## Additional Resources
+
+- ServiceNow Client Script Best Practices
+- GlideAjax Documentation
+- Client-Side Scripting API Reference
+- Performance Optimization Guide