🔍Mastering Client Scripts in ServiceNow: Key Methods, Best Practices & Advanced Use Cases

[Bhavesh Patil]

Client Scripts are one of the most powerful tools available to ServiceNow developers for enhancing user experience directly within the browser. By manipulating form elements dynamically and responding to user input in real time, they help build smarter, more responsive applications.

In this post, I’ll walk through essential methods (g_form, g_user), real-world advanced use cases, and debugging tips to take your client-side development to the next level.

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🧠 Quick Recap: Types of Client Scripts

• onLoad – Runs when the form is loaded

• onChange – Triggers when a specific field changes

• onSubmit – Executes just before the form is submitted

• onCellEdit – Runs when a cell is edited in list view

💡 These scripts run in the browser, so always keep them lightweight and fast.

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🔧 Commonly Used Methods

🎯 g_form (Form Controls)

getValue(field_name)
setValue(field_name, value)
setDisplay(field_name, true|false)
setMandatory(field_name, true|false)
setReadOnly(field_name, true|false)
showFieldMsg(field_name, message, 'info'|'error')
clearValue(field_name)
isVisible(field_name)
addOption(field_name, value, label)
removeOption(field_name, value)

👤 g_user (User Context)

g_user.hasRole(role)
g_user.userID
g_user.name

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🧩 Advanced Client Script Use Cases Every ServiceNow Developer Should Know

🔐 1. Lock Fields After First Save

Use Case: Prevent edits to key fields after initial record creation.

function onLoad() {
  if (!g_form.isNewRecord()) {
    g_form.setReadOnly('short_description', true);
    g_form.setReadOnly('category', true);
  }
}

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✅ 2. Hide All Fields on Form Load

function onLoad() {
  var allFields = g_form.getEditableFields();
  for (var i = 0; i < allFields.length; i++) {
    g_form.setDisplay(allFields[i], false);
  }
}

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🧑‍💼 3. Role-Based Option Filtering

Use Case: Control dropdown options based on user roles or responsibilities.

function onLoad() {
  if (!g_user.hasRole('admin')) {
    g_form.removeOption('impact', '1'); // High
    g_form.removeOption('impact', '2'); // Medium
    g_form.addOption('impact', '3', 'Low Only (Restricted)');
  }
}

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🔍 4. Validate Reference Field Based on Department

Use Case: Prevent misassignment based on reference field data validation.

function onSubmit() {
  var selectedUser = g_form.getValue('assigned_to');
  var gr = new GlideRecord('sys_user');
  if (gr.get(selectedUser)) {
    if (gr.getValue('department') !== 'd3b2b0c1db98b0104d5c3a7e0f9619b6') {
      g_form.showFieldMsg('assigned_to', 'User must be from IT Support.', 'error');
      return false;
    }
  }
  return true;
}

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🧩 5. Section Visibility and Field Restrictions by Role

Use Case: Ensure only certain roles can access sensitive form sections.

function onLoad() {
  if (!g_user.hasRole('itil_admin')) {
    g_form.setSectionDisplay('Advanced Options', false);
    g_form.setReadOnly('impact', true);
    g_form.setReadOnly('urgency', true);
  }
}

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🕓 6. Time-Based Form Logic (Business Hours)

Use Case: restrict actions outside SLA/working timeframes.

function onLoad() {
  var now = new Date();
  var day = now.getDay();
  var hour = now.getHours();

  var isWorkingHour = (day >= 1 && day <= 5) && (hour >= 8 && hour <= 18);

  if (!isWorkingHour) {
    g_form.addInfoMessage('You are submitting this request outside business hours. Processing may be delayed.');
    g_form.setReadOnly('assignment_group', true);
    g_form.setReadOnly('priority', true);
  }
}

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🚨 Pitfalls to Avoid

• ❌ Don’t put server-side logic in Client Scripts

• ❌ Don’t use g_form in Business Rules or Script Includes

• ❌ Avoid long or synchronous operations — it slows the UI

• ❌ Don’t forget mobile/responsive view testing

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🧪 Debugging Tips (for Client Scripts)

• ✅ Use console.log() to inspect values

console.log(\"Assigned To: \" + g_form.getValue('assigned_to'));

• 🐞 Use Field Watcher
  Right-click → Watch – Field Value Change

• ⏱️ Use Script Stressors for Load Testing:

• 🔍 Use browser Dev Tools (F12) to see errors and logs live

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🏁 Final Thoughts

Client Scripts are essential to building responsive, intelligent UIs in ServiceNow. But they should be carefully designed with performance, user roles, and UX in mind.

Keep experimenting, and always test across form views and devices!

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👉 How do you use Client Scripts to solve complex problems?
Share your tricks, gotchas, and creative patterns in the comments!

If this helped, please mark it as Correct or Helpful—it really means a lot!

[ererg]

Great, Excellent summary

[vishvas]

Really appreciate this breakdown, tips was especially helpful! 

[ganeshbagul]

Excellent summary