Hey @UdayG0047661101
In ServiceNow, Client Scripts are used to perform actions on forms in the user's browser without requiring a server call. They help improve user experience by validating data, controlling field behavior, and responding to user interactions.
There are 4 types of Client Scripts:
1. OnLoad Client Script
Purpose:
Runs automatically when a form is loaded.
Common Use Cases:
- Make fields read-only
- Hide or show fields
- Set default values
- Display informational messages
Structure:
function onLoad() {
// Code executes when form loads
}
Example:
function onLoad() {
g_form.setReadOnly('priority', true);
g_form.addInfoMessage('Welcome to the Incident form.');
}
2. OnChange Client Script
Purpose:
Runs whenever the value of a specified field changes.
Common Use Cases:
- Dynamic field validation
- Auto-populating fields
- Showing or hiding fields based on selections
Structure:
function onChange(control, oldValue, newValue, isLoading, isTemplate) {
if (isLoading || newValue === '') {
return;
}
// Your logic here
}
Example:
function onChange(control, oldValue, newValue, isLoading, isTemplate) {
if (isLoading || newValue == '') {
return;
}
if (newValue == '1') {
g_form.showFieldMsg('priority',
'High Priority selected',
'info');
}
}
3. OnSubmit Client Script
Purpose:
Runs when the user clicks Submit, Update, Save, Order Now, etc.
Common Use Cases:
- Form validation before submission
- Preventing record save when required conditions are not met
Structure:
function onSubmit() {
// Validation logic
return true; // Allow submission
}
Example:
function onSubmit() {
if (g_form.getValue('short_description') == '') {
g_form.addErrorMessage(
'Short Description is mandatory.'
);
return false;
}
return true;
}
4 . OnCellEdit Client Script
Purpose:
Runs when a cell value is edited in a List View.
Common Use Cases:
- Validate list edits
- Restrict invalid updates in list editing
Structure:
function onCellEdit(sysIDs, table, oldValues, newValue, callback) {
// Validation logic
callback(true);
}
Example:
function onCellEdit(sysIDs, table, oldValues, newValue, callback) {
if (newValue == " '') {
alert('Value cannot be empty');
callback(false);
return;
}
callback(true);
}
Best Practice:
- Use Client Scripts only for UI-related logic.
- Avoid heavy processing on the client side.
- Use GlideAjax when server-side data is required.
- Keep scripts lightweight for better form performance.
Official documentation also provides detailed guidance on Client Script types, execution order, and best practices within the platform.
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If this response helps, please mark it as Accept as Solution and Helpful.
Doing so helps others in the community and encourages me to keep contributing.
Regards
Vaishali Singh
Servicenow Developer
Linkedin - https://www.linkedin.com/in/vaishali-singh-2273361bb
