ServiceNow field guide

GlideAjax, Simplified

Learn GlideAjax with simple analogies and a visual lab to understand the exchange between Client Script, GlideAjax, and Script Include.

Itallo Brandão Nov 28, 2025

First check: is there Low-code or OOTB?

Before spinning up a GlideAjax or any hardcoded solution, be brutally honest: does the platform already solve this? A Flow Designer, Integration Hub, Data Lookup, or even an OOTB component often delivers 80–100% of the requirement with far less effort and maintenance.

  • 1
    Map the requirement: describe what the user needs, process context, and the rules already in place.
  • 2
    Inventory your options: review OOTB catalogs, Store apps, and low-code resources before drafting a custom architecture.
  • 3
    Justify the custom build: if you still need code, document the reasons (functional gaps, performance, compliance) and proceed intentionally.

That discipline saves time, keeps you aligned with ServiceNow best practices, and avoids needless legacy. When OOTB/low-code can’t cover it, that’s the moment to go hardcode.

Important

For learning purposes I picked a very simple scenario: fetching the user’s email via script. In a real project you’d solve this with Dot-Walking (showing related table fields) instead of coding. I chose this flow because it is clear and lightweight, so we can focus 100% on GlideAjax syntax without complex business logic distractions.

Why GlideAjax exists

GlideAjax is the safe bridge between the Client Script and the Script Include. It lets you pull server data without freezing the UI, respects ACLs, and cuts unnecessary backend calls.

  • 1
    Performance: asynchronous calls keep the user working while the response is on its way.
  • 2
    Security: Script Include ACLs stay in charge and block direct DB access.
  • 3
    Flexibility: return strings, JSON objects, or whatever payload the client must render.

Concept: The Asynchronous Waiter

The browser (Client Side) cannot touch the database directly for security and performance reasons. To request data from the server without reloading or freezing the page, we use GlideAjax as the middle person.

1. Client (Table)
You (Client Script) place the order at the table. No direct access to the kitchen (Database).

2. GlideAjax (Waiter)
Carries the order (parameters) and brings back the dish (XML/JSON). The guest keeps chatting while they wait (asynchronous).

3. Server (Kitchen)
The Chef (Script Include) receives the order, queries the stock (DB) safely, and prepares the response.

GlideAjax Interactive Lab

Test GlideAjax below. Change the Caller field and watch the kitchen animation plus the logs happening in real time.

Heads-up: The simulator below is a purely visual illustration (plain HTML/JS). Real GlideAjax code only runs inside a ServiceNow instance.
Incident: INC0010042 (New Record)
Debug Timeline

Waiting for a change on the form...
I need that email!
Client
Client Script
On my way!
Waiter
GlideAjax
Looking it up...
Cook
Script Include

Rotate the screen to use the simulator

Almost there! This device has enough height—just switch it to landscape to unlock the GlideAjax interactive lab.

Simulator available only on tall screens

To experience the interactive lab, open this guide on a device with at least 900 px of height (desktop, laptop, or tablet in landscape). You can still follow the full theory on mobile.

Step 1: The Backend (Script Include)

How to create it in ServiceNow

  • 1
    Navigate to System Definition > Script Includes.
  • 2
    Click New.
  • 3
    Set the Name (e.g., UserDataHelper). Keep it handy!
  • 4
    IMPORTANT: Check Client callable. Without it, the browser can’t call this script.
Script Include: UserDataHelper Server-Side (JavaScript) 
var UserDataHelper = Class.create();
UserDataHelper.prototype = Object.extendsObject(AbstractAjaxProcessor, {

    // Function name exposed to the client
    getEmail: function() {
        
        // 1. Capture the parameter (snake_case by convention)
        var userId = this.getParameter('sysparm_user_id');
        if (!userId) return '';
        
        // 2. Use GlideRecord to query the target table
        var gr = new GlideRecord('sys_user');
        
        if (gr.get(userId)) {
            // 3. Return the value via getValue (more performant)
            return gr.getValue('email') || '';
        }
        
        return '';
    },

    type: 'UserDataHelper'
});

Step 2: The Frontend (Client Script)

How to create it in ServiceNow

  • 1
    Go to System Definition > Client Scripts.
  • 2
    Click New.
  • 3
    Fill out: Table = Incident, Type = onChange, Field name = Caller.
Client Script Client-Side (JavaScript) 
function onChange(control, oldValue, newValue, isLoading) {
    if (isLoading) return;

    // 1. Clear the field if the user removes the caller (avoid orphan data)
    if (newValue === '') {
        g_form.setValue('u_email', '');
        return;
    }

    // 2. Instantiate GlideAjax with the Script Include NAME
    var ga = new GlideAjax('UserDataHelper');
    
    // 3. Tell it which FUNCTION to run
    ga.addParam('sysparm_name', 'getEmail');
    
    // 4. Send the parameters (use consistent naming)
    ga.addParam('sysparm_user_id', newValue);
    
    // 5. Fire the async call (getXMLAnswer is the modern default)
    ga.getXMLAnswer(function(answer) {
        // Guard against null/undefined
        g_form.setValue('u_email', answer || '');
    });
}
Pro tip: Avoid ga.getXMLWait(). It locks the user’s browser until the server answers and creates terrible UX.

Golden Tips

  • 1
    Use getXMLAnswer: Back then we used getXML and had to parse XML manually. getXMLAnswer already returns the clean string.
  • 2
    JSON for complex payloads: Need to send Email, Phone, and Title together? Don’t fire three GlideAjax calls. Return one JSON object (JSON.stringify) and parse it on the client (JSON.parse).

Reference material

Explore official docs and community content to deepen your GlideAjax knowledge and keep your implementations aligned with platform best practices.

  • Official documentation

    The latest ServiceNow GlideAjax documentation covering methods, parameters, and examples.

    Open
  • Community article on GlideAjax

    Great article by Shawn Dowler with a practical example and a clean explanation of the parameters.

    Open

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