Client scripts · SN Doc Reader

Client scripts allow the system to run JavaScript on the client (web browser) when client-based events occur, such as when a form loads, after form submission, or when a field changes value.

Use client scripts to configure forms, form fields, and field values while the user is using the form. Client scripts can:

make fields hidden or visible
make fields read only or writable
make fields optional or mandatory based on the user's role
set the value in one field based on the value in other fields
modify the options in a choice list based on a user's role
display messages based on a value in a field

Warning:

Client scripts are intended to optimize the user experience on a form. Client scripts are not meant to protect unwanted access to data.

To prevent unwanted access to data, ensure that sensitive fields are hidden or read-only through ACLs or data policies.

For more information, see Access Control Lists (ACLs) or Data policy.

Where client scripts run

With the exception of onCellEdit() client scripts, client scripts only apply to forms and search pages. If you create a client script to control field values on a form, you must use one of these other methods to control field values when on a list.

Create an access control to restrict who can edit field values.
Create a business rule to validate content.
Create a data policy to validate content.
Create an onCellEdit() client script to validate content.
Disable list editing for the table.

Note: Client scripts are not supported on ServiceNow mobile applications.

Parent Topic:Writing client-side scripts

Related topics

Client API reference

Create a client script

Create a client script to control form behavior, respond to field changes, validate submissions, or update cell values in a list.

Before you begin

Role required: admin

Procedure

Navigate to System Definition > Client Scripts.
Select New.
Complete the form.

Field	Description
Name	Name of the client script.
Table	Table to which the client script applies.
UI Type	Target user interface to which the client script applies. - Desktop: The script runs only in the desktop Core UI. Mobile / Service Portal: The script runs only in mobile, portal, or configurable workspace UIs. All: The script runs across all available UIs. Note: Client scripts that run on forms in the Service Portal or mobile environments can only include certain APIs. For more information, see Client-side scripting for mobile.
Type	onLoad() — runs when the system first renders the form and before users can enter data. Typically, onLoad() client scripts perform client-side manipulation of the current form or set default record values. onSubmit() — runs when a form is submitted. Typically, onSubmit() scripts validate form content and confirm that the submission makes sense. An onSubmit() client script can cancel form submission by returning a value of false. onChange() — runs when a particular field value changes on the form. The onChange() client script must specify these parameters. control: the DHTML widget whose value changed. Note: control is not accessible in mobile and service portal. oldValue: the value the widget had when the record was loaded. Note: Old values aren't returned for the HTML field type. newValue: the value the widget has after the change. isLoading: identifies whether the change occurs as part of a form load. isTemplate: identifies whether the change occurs as part of a template load. onCellEdit() — runs when the list editor changes a cell value. The onCellEdit() client script must specify these parameters. sysIDs: an array of the sys_ids for all items being edited. table: the table of the items being edited. oldValues: the old values of the cells being edited. newValue: the new value for the cells being edited. callback: a callback that continues the execution of any other related cell edit scripts. If true is passed as a parameter, the other scripts run or the change is committed if there are no more scripts. If false is passed as a parameter, further scripts are not run and the change is not committed.
Field Name	Name of the field to which the script applies. Available only if the script responds to a field value change (onChange or onCellEdit script types).
Application	Application where this client script resides.
Active	Enables the client script when selected. Clear this field to disable the client script.
Inherited	Indicates whether the client script applies to extended tables.
Global	When selected, the client script runs on all views of the table.
View	Available only when Global is cleared. Views on which the client script runs.
Description	Description of the functionality and purpose of the client script.
Messages	Text string (one per line) available to the client script as localized messages using getmessage('[message]'). For more information, see Translate a client script message.
Script	Contains the client script.
Isolate script	New client scripts run in strict mode, in which direct DOM access is turned off. Access to jQuery, prototype, and the window object are also turned off by default. To enable DOM access on a per-script basis, clear the Isolate script check box. To turn off strict mode for all new globally scoped client scripts, set the glide.script.block.client.globals system property to false.

4. Select **Submit**.

Get the value of a variable

Use the following syntax to obtain the value of a catalog variable. Note that the variable must have a name. Replace variable_name with the name of the variable.

JavaScript

g_form.getValue('variable_name');

Restrict the number of characters a user can type in a variable

This is an example of a script that runs when the variable is displayed, rather than when the item is ordered.

JavaScript

function onLoad(){  var sd = g_form.getControl('short_description');  sd.maxLength=80;}

title	Client scripts
description	Client scripts allow the system to run JavaScript on the client \(web browser\) when client-based events occur, such as when a form loads, after form submission, or when a field changes value.Create a client script to control form behavior, respond to field changes, validate submissions, or update cell values in a list.
locale	en-US
canonical_url	https://www.servicenow.com/docs/r/australia/api-reference/scripts/client-scripts.html
release	australia
product	Scripts
classification	scripts
topic_type	concept
last_updated	2026-09-10
reading_time_minutes	5
keywords	client scriptcreate client script
breadcrumb	Write client-side scriptsScriptingAPI implementationAPI implementation and reference