Set a field value in a Client Script

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Instance:sourdoughdev·Version:Yokohama

Instance StateONLINE

System StatusFully Operational

Session Timeout90 minutes

Logged-In Sessions2 (20 active)

Build Nameyokohama-12-18-2024_p1

IP Address10.159.128.43

Instance HealthHealth Score: 90%

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Programmatically set the value of a form field from a Client Script

Client Script

function onChange(control, oldValue, newValue, isLoading) {
    if (isLoading || newValue === '') {
        return;
    }
    
    // String field - direct value assignment
    g_form.setValue('short_description', 'Automatically generated incident');
    
    // Boolean field - pass boolean or string
    g_form.setValue('active', true);
    g_form.setValue('made_sla', 'false');
    
    // Choice field - use the actual choice value
    g_form.setValue('state', '2'); // In Progress
    g_form.setValue('priority', '3'); // Moderate
    
    // Reference field - requires sys_id and display value
    var assignedToSysId = '5137153cc611227c000bbd1bd8cd2005';
    var assignedToName = 'Abel Tuter';
    g_form.setValue('assigned_to', assignedToSysId, assignedToName);
    
    // Date/datetime field - use proper format
    var futureDate = new Date();
    futureDate.setDate(futureDate.getDate() + 7);
    g_form.setValue('due_date', futureDate.toISOString().split('T')[0]);
    
    // Clear a field by setting to empty string
    g_form.setValue('work_notes', '');
}

The g_form.setValue() method is how you programmatically change field values in the browser without triggering a server round-trip. The critical gotcha most developers miss: reference fields require both the sys_id as the value AND the display value as a second parameter — otherwise the field shows the GUID to users. Choice fields need the actual choice value (like '2' for state), not the display label. This is different from server-side scripting where you can often be more flexible with value types.

When to use this

In onChange client scripts when one field change should automatically populate other fields
In onLoad client scripts to set default values based on user roles or URL parameters
In UI Action client scripts before form submission to populate hidden calculation fields
When you need immediate visual feedback without waiting for server processing

When NOT to use this

Don't use in onSubmit client scripts for validation — the values won't be saved to the database, use Business Rules instead
Don't use to set values that require server-side data lookups — use GlideAjax to fetch the data first
Don't use for fields that should trigger their own onChange events if you want those events to fire — use g_form.setValue() with the third parameter true instead
Don't use on read-only fields or fields the current user doesn't have write access to — it will silently fail

Key behaviors and gotchas

Reference fields require sys_id as first parameter and display value as second: g_form.setValue('assigned_to', sysId, displayName)
Choice fields need the actual choice value ('2'), not the display label ('In Progress')
Boolean fields accept both actual booleans and string values (true or 'true')
Date fields expect YYYY-MM-DD format, datetime fields expect full ISO format or ServiceNow internal format
Setting a field to empty string ('') clears the field completely
The method bypasses field validation and onChange scripts by default — add true as third parameter to trigger onChange events
Values set in client scripts don't persist unless the form is saved — they're only visual changes in the browser

⚠️

Never call setValue() in an onChange script for the same field that triggered the onChange — you'll create an infinite loop that crashes the browser tab.

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Alternative Approaches

Direct DOM manipulation

// Direct DOM access - not recommended but sometimes necessary
function onChange(control, oldValue, newValue, isLoading) {
    if (isLoading) return;
    
    // Only use when g_form.setValue doesn't work for complex widgets
    var fieldElement = document.getElementById('sys_display.incident.assigned_to');
    if (fieldElement) {
        fieldElement.value = 'Abel Tuter';
        // Must also set the hidden sys_id field
        document.getElementById('incident.assigned_to').value = '5137153cc611227c000bbd1bd8cd2005';
    }
}

Use only when g_form.setValue() doesn't work with custom widgets or complex field types.

Trade-offs: Bypasses all ServiceNow field handling and can break with platform upgrades.

API Methods Used

GlideForm.getValue()GlideForm.clearValue()GlideForm.setReadOnly()GlideForm.setMandatory()

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