ServiceNow Client Script

You are a ServiceNow platform developer. The user wants to write client scripts that manipulate forms using onChange, onLoad, and onSubmit events.

What to check first

• Verify you're in the correct ServiceNow instance and have access to the table where you'll create the client script
• Check that the form you're targeting exists by navigating to the table module and opening a record
• Confirm the field names you plan to manipulate by inspecting the form or checking the table schema (Settings > Fields & Columns)

Steps

1. Navigate to System Definition > Client Scripts in your ServiceNow instance
2. Click New to create a client script record
3. Fill in the Table field with the target table name (e.g., incident, change_request)
4. Set the UI Type to Desktop (or Mobile if needed)
5. Choose the Type dropdown and select one of: onLoad, onChange, onSubmit
6. Enter the target Field name if using onChange; leave blank for onLoad/onSubmit
7. Write your script logic in the Script field using the g_form API object
8. Check Active to enable the script immediately
9. Click Submit to save; test by loading or interacting with the form

Code

// CLIENT SCRIPT - onLoad Example
function onLoad() {
  // Get current user info
  var currentUser = g_user.getID();
  var userName = g_user.getName();
  
  // Set field values on form load
  g_form.setValue('assigned_to', currentUser);
  
  // Show/hide fields based on conditions
  if (g_form.getValue('priority') === '1') {
    g_form.setVisible('escalation_reason', true);
  } else {
    g_form.setVisible('escalation_reason', false);
  }
  
  // Make field mandatory
  g_form.setMandatory('urgency', true);
  
  // Disable field
  g_form.setDisabled('state', true);
}

// CLIENT SCRIPT - onChange Example
function onChange(control, oldValue, newValue, isLoading) {
  // Only execute if form is fully loaded (not during initial load)
  if (isLoading) {
    return;
  }
  
  // Trigger when 'category' field changes
  if (control.getName() === 'category') {
    // Update dependent field
    if (newValue === 'hardware') {
      g_form.setValue('subcategory', '');
      g_form.setMandatory('asset_tag', true);
      g_form.setLabel('asset_tag', 'Asset Tag (Required)');
    } else if (newValue === 'software') {
      g_form.setMandatory('asset_tag', false);
      g_form.setLabel('asset_tag', 'Asset Tag');

Note: this example was truncated in the source. See the GitHub repo for the latest full version.

Common Pitfalls

• Treating this skill as a one-shot solution — most workflows need iteration and verification
• Skipping the verification steps — you don't know it worked until you measure
• Applying this skill without understanding the underlying problem — read the related docs first

When NOT to Use This Skill

• When a simpler manual approach would take less than 10 minutes
• On critical production systems without testing in staging first
• When you don't have permission or authorization to make these changes

How to Verify It Worked

• Run the verification steps documented above
• Compare the output against your expected baseline
• Check logs for any warnings or errors — silent failures are the worst kind

Production Considerations

• Test in staging before deploying to production
• Have a rollback plan — every change should be reversible
• Monitor the affected systems for at least 24 hours after the change