Client Scripts are a fundamental component in ServiceNow that execute JavaScript code on the client-side (user's web browser) rather than on the server. They are used to enhance the user experience by providing real-time validation, field manipulation, and dynamic form behavior when users interact …Client Scripts are a fundamental component in ServiceNow that execute JavaScript code on the client-side (user's web browser) rather than on the server. They are used to enhance the user experience by providing real-time validation, field manipulation, and dynamic form behavior when users interact with forms.
There are four main types of Client Scripts:
1. **onLoad**: Executes when a form is first loaded. This is useful for setting default values, hiding or showing fields, or making fields mandatory based on certain conditions when the record opens.
2. **onChange**: Triggers when a specific field value changes. This allows developers to create dynamic responses, such as populating related fields, showing alerts, or modifying form elements based on user input.
3. **onSubmit**: Runs when a user attempts to save or submit a form. This type is commonly used for validation purposes, ensuring required data is entered correctly before the record is saved to the database.
4. **onCellEdit**: Executes when a cell is edited in a list view, enabling validation and manipulation at the list level.
Key considerations when working with Client Scripts include:
- **Performance**: Since they run in the browser, excessive or poorly written Client Scripts can slow down form loading and user interactions.
- **g_form API**: ServiceNow provides the GlideForm API (g_form) for interacting with forms, allowing developers to get and set field values, show or hide fields, and display messages.
- **g_user API**: This provides access to current user information like name, roles, and user ID.
- **Best Practices**: Keep Client Scripts lightweight, use UI Policies for simple show/hide and mandatory requirements, and avoid unnecessary server calls.
Client Scripts are essential for creating intuitive, responsive forms that guide users through data entry while maintaining data quality and improving overall system usability.
Client Scripts in ServiceNow
Why Client Scripts Are Important
Client Scripts are essential in ServiceNow because they provide real-time interactivity and responsiveness on forms. They execute in the user's web browser, allowing for instant feedback and validation before data is submitted to the server. This improves user experience by reducing unnecessary server calls and providing immediate guidance to users filling out forms.
What Are Client Scripts?
Client Scripts are JavaScript code that runs on the client side (in the user's browser) when a form is loaded or when specific events occur on a form. They are used to:
• Validate field entries before submission • Set field values dynamically • Show or hide form sections • Make fields mandatory or read-only • Display alerts or confirmations to users
Types of Client Scripts
There are four main types of Client Scripts you must know:
1. onLoad - Executes when a form is first loaded. Used to set initial field values or modify the form appearance.
2. onChange - Executes when a specific field value changes. Requires you to specify which field to monitor.
3. onSubmit - Executes when a user submits the form. Used for validation before the record is saved. Can prevent submission by returning false.
4. onCellEdit - Executes when a field value is changed using list editing in a list view.
How Client Scripts Work
Client Scripts use the GlideForm API (commonly referenced as g_form) to interact with form elements. Common methods include:
• g_form.getValue('field_name') - Gets a field's value • g_form.setValue('field_name', 'value') - Sets a field's value • g_form.setMandatory('field_name', true/false) - Makes a field required • g_form.setVisible('field_name', true/false) - Shows or hides a field • g_form.setReadOnly('field_name', true/false) - Makes a field read-only • g_form.addErrorMessage('message') - Displays an error message • g_form.showFieldMsg('field_name', 'message', 'info') - Shows a message near a field
Key Characteristics
• Client Scripts only run on forms, not in list views (except onCellEdit) • They do not execute during web service calls or background operations • They run in the browser, so they affect only the current user's session • Multiple Client Scripts can exist for the same table and event
Exam Tips: Answering Questions on Client Scripts
Tip 1: Remember that Client Scripts are client-side only. If a question asks about background processing or server-side validation, Client Scripts are not the answer.
Tip 2: Know which script type to use for each scenario. Form loading scenarios need onLoad. Field change scenarios need onChange. Pre-submission validation needs onSubmit.
Tip 3: onSubmit scripts must return false to prevent form submission. If a question mentions stopping a submission based on validation, look for answers involving onSubmit returning false.
Tip 4: onChange scripts require a field name to be specified. If an exam question mentions reacting to a specific field modification, onChange is the correct type.
Tip 5: Client Scripts do not run during imports, web services, or scheduled jobs. For those scenarios, Business Rules are appropriate.
Tip 6: The g_form object is exclusive to Client Scripts. If you see g_form in answer options, you are dealing with client-side functionality.
Tip 7: Pay attention to whether a question asks about form-based or list-based changes. Standard Client Scripts work on forms; onCellEdit works on list edits.