Calling Server Side Code from Client Script using GlideAjax in ServiceNow

Introduction

GlideAjax is a powerful tool in ServiceNow that enables client scripts to communicate asynchronously with server-side Script Includes. This is especially useful when retrieving data from the server without requiring a page refresh.

In this blog, we will explore how to use the getXML(), getXMLWait(), and getXMLAnswer() methods to call server-side functions using GlideAjax.

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1. Using getXML() (Asynchronous – Preferred)

This method sends a request to the server and processes the response using a callback function.

function onChange(control, oldValue, newValue, isLoading) {
    if (isLoading || newValue == '') {
        return;
    }
    var ga = new GlideAjax('SampleScriptInclude');
    ga.addParam('sysparm_name', 'getServerMessage');
    ga.getXML(parseResponse);
    
    function parseResponse(response) {
        var answer = response.responseXML.documentElement.getAttribute("answer");
        alert("Response from server: " + answer);
    }
}

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2. Using getXMLWait() (Synchronous – Not Recommended)

This method waits for the server response, blocking execution, which can impact performance.

function onChange(control, oldValue, newValue, isLoading) {
    if (isLoading || newValue == '') {
        return;
    }
    var ga = new GlideAjax('SampleScriptInclude');
    ga.addParam('sysparm_name', 'getServerMessage');
    var response = ga.getXMLWait();
    var answer = response.responseXML.documentElement.getAttribute("answer");
    alert("Response from server: " + answer);
}

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3. Using getXMLAnswer() (Asynchronous & Cleaner)

This method returns only the answer attribute, making response handling simpler and cleaner.

function onChange(control, oldValue, newValue, isLoading) {
    if (isLoading || newValue == '') {
        return;
    }
    var ga = new GlideAjax('SampleScriptInclude');
    ga.addParam('sysparm_name', 'getServerMessage');
    ga.getXMLAnswer(function(answer) {
        alert("Response from server: " + answer);
    });
}

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Server-Side Script Include (Used for All Examples)

The following Script Include processes the request from the client script and returns a response:

var SampleScriptInclude = Class.create();
SampleScriptInclude.prototype = Object.extendsObject(AbstractAjaxProcessor, {
    getServerMessage: function() {
        return "Hello from Server-Side!";
    }
});

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Comparison Table

Method	Type	Blocking Execution?	Recommended?	Notes
getXML()	Asynchronous	No	Yes	Uses a callback function to process the XML response.
getXMLWait()	Synchronous	Yes	No	Blocks execution, which can cause performance issues.
getXMLAnswer()	Asynchronous	No	Yes	Returns only the answer attribute, simplifying response handling.

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Which One Should You Use?

• Use getXMLAnswer() if your Script Include returns a single answer attribute.
• Use getXML() if you need to process an XML response.
• Avoid getXMLWait() unless absolutely necessary, as it blocks execution and can degrade performance.

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Conclusion

Using GlideAjax, you can efficiently fetch and display data from the server without refreshing the page. The choice of method depends on whether you need XML processing or a direct response.

To enhance performance and improve user experience, always prefer asynchronous methods like getXML() and getXMLAnswer().

Let us know in the comments which method you prefer and why! 🚀