💻 Client Scripts in ServiceNow

🌐 1. Introduction

Client Scripts are pieces of JavaScript that run in the user’s browser (client-side) when interacting with forms and fields in ServiceNow.

They are used to:

• Control form behavior dynamically

• Validate field values before submission

• Improve the user experience (UX) by reducing server calls

📑 2. Types of Client Scripts

1. onLoad()

   • Runs when a form loads.

   • Example: Hide the “VIP” checkbox for non-admins.

2. onChange()

   • Runs when a field value changes.

   • Example: If Priority = 1, auto-populate Impact = High.

3. onSubmit()

   • Runs when the user clicks Submit/Update.

   • Can validate or block submission.

   • Example: Prevent form submission if “Short Description” is empty.

4. onCellEdit()

   • Runs when a list field is edited inline.

   • Example: Validate that SLA date is not set in the past when editing list rows.

⚡ 3. Client Script Examples

Example 1: onLoad Script

function onLoad() {
   if (g_user.hasRole('itil') == false) {
       g_form.setVisible('vip', false); // Hide VIP field for non-ITIL users
   }
}

Example 2: onChange Script

function onChange(control, oldValue, newValue) {
   if (newValue == '1') {
       g_form.setValue('impact', '1'); // High impact if Priority = Critical
   }
}

Example 3: onSubmit Script

function onSubmit() {
   if (g_form.getValue('short_description') == '') {
       alert("Short Description is mandatory!");
       return false; // Prevent submission
   }
   return true;
}

Example 4: onCellEdit Script

function onCellEdit(sysIDs, table, oldValues, newValue) {
   if (newValue < gs.nowDateTime()) {
       alert("SLA Date cannot be set in the past!");
       return false;
   }
   return true;
}

🔍 Advanced Concepts

• g_form API

  • Used to manipulate fields in forms (setValue, setVisible, setMandatory, etc.).

• g_user API

  • Used to check current user roles, groups, or properties.

• Client Callable Script Includes

  • Used when Client Script needs server-side data without refreshing the page.

  • Called using GlideAjax.

  var ga = new GlideAjax('UserInfo');
  ga.addParam('sysparm_name', 'getManager');
  ga.addParam('sysparm_user', g_form.getValue('caller_id'));
  ga.getXMLAnswer(function(response) {
      g_form.setValue('manager', response);
  });
  

• Best with UI Policies

  • Use UI Policies whenever possible (simpler and faster).

  • Use Client Scripts only when advanced logic is required.

🛠️  Real-World Use Cases

1. Incident Form: Auto-populate Impact and Urgency based on Priority.

2. Change Request: Prevent submission unless Risk is assessed.

3. HR Case Form: Hide sensitive fields unless the user is in the HR group.

4. Service Catalog Item: Auto-calculate cost when quantity changes.

5. CMDB Form: Validate serial numbers follow a specific pattern.

💡  Best Practices

• ✅ Use UI Policies first—they are simpler and more efficient.

• ✅ Write modular scripts—avoid hardcoding values.

• ✅ Document Client Scripts for future maintenance.

• ✅ Use GlideAjax instead of g_form.submit() for server calls.

• ✅ Test in sub-production environments before going live.

• ❌ Avoid excessive Client Scripts—they slow down form performance.

• ❌ Don’t duplicate logic between Client Scripts and Business Rules.

🎬 Conclusion

Client Scripts in ServiceNow make forms dynamic and interactive, improving the end-user experience.

• onLoad, onChange, onSubmit, and onCellEdit scripts provide flexibility for different use cases.

• Combined with g_form, g_user, and GlideAjax, Client Scripts can deliver powerful, real-time validation and automation.