ServiceNow Client Scripting

Quick start

GlideAjax pattern (async, non-blocking):

function makeServerCall() {
    // Always check if already loading
    if (isLoading || g_form.getValue('field') === '') {
        return;
    }
    
    var ga = new GlideAjax('ScriptIncludeName'); // PascalCase
    ga.addParam('sysparm_name', 'methodName');
    ga.addParam('sysparm_data', g_form.getValue('source_field'));
    
    // MUST use getXMLAnswer (async), NEVER getXMLWait
    ga.getXMLAnswer(function(answer) {
        if (answer) {
            g_form.setValue('target_field', answer);
        }
    });
}

Critical rules

Performance optimization

Use g_scratchpad (server → client on load):

// Display Business Rule (server):
g_scratchpad.vip = true;

// OnLoad script (client):
if (g_scratchpad.vip) {
    g_form.setLabel('priority', 'VIP Priority');
}

Avoid redundant calls:

// ✓ CORRECT: Check client logic first
if (!isLoading && newValue) {
    // Make server call
}

// Set display value to avoid round-trips
g_form.setValue('ref_field', id, displayValue);

Best practices

• Use UI Policies for visibility/mandatory/read-only logic
• Always check isLoading flag before GlideAjax calls
• Use setValue(field, id, display) to avoid extra queries
• Avoid global variables; scope to specific tables
• Test with all form layouts before production

Key APIs

Reference

For GlideAjax templates, g_scratchpad patterns, and examples, see BEST_PRACTICES.md