Prototypical Inheritance in JavaScript: A Look at Prototype JS in ServiceNow

Prototype JS is an open-source JavaScript framework. Sam Stephenson first developed the project in February of 2005. As of March 2021, according to w3techs, Prototype is used by 0.6% of all websites. This 0.6 % includes ServiceNow, the cloud platform I currently work with for application development. When using Prototype JS, we take the complexity out of client-side web programming since it includes shortcuts to major functions for dealing with XMLHttpRequest. In JavaScript, the fundamental data type is the Object. An Object is a collection of properties, each of which has a name and a value. But in addition to maintaining its own set of properties, in JavaScript, objects inherit the properties of another object; this is what we know as its “Prototype,” and this prototypical inheritance is an essential feature of JavaScript. Prototype JS takes this prototype concept even further, including syntax that simulates the classic heritage of object-oriented programming — This is fascinating. I discovered prototype JS when I first started working with the ServiceNow platform back in 2013. At that moment, I was working on a requirement for a customer that involved creating a client script that sent parameters to the server. The GlideAjax Class allowed me to execute the server-side code from the client, and then I stumble upon Class.create().

Class.create()Creates a class, then returns a constructor function for instances of the same class. Then, we can pass a class as an argument. In this case, it's used as the new Class's superclass and will inherit all its methods. Any other elements that we pass as arguments get treated as objects.

In ServiceNow, a Client Script code using GlideAjax. Script query the table incident and return the short description as an alert window.function onChange(control, oldValue, newValue, isLoading, isTemplate) {
if (isLoading || newValue === '') {
return;
}var ga = new GlideAjax('HelloWorld');
ga.addParam('sysparm_name', 'helloWorld');
ga.addParam('sysparm_number', g_form.getValue('number'));
ga.getXML(HelloWorldParse);function HelloWorldParse(response) {
var answer = response.responseXML.documentElement.getAttribute("answer");
alert(answer);
}}

The Script Include we called from the client script. Noting line # 1, for the use of Class.create().var HelloWorld = Class.create();
HelloWorld.prototype = Object.extendsObject(AbstractAjaxProcessor, {
helloWorld: function() {
var incNum = this.getParameter('sysparm_number');
var gr = GlideRecord('incident');
gr.addQuery('number', incNum);
gr.query();
if (gr.next()) {
var incDesc =gr.short_description;
return incDesc;
}
},
_privateFunction: function() {
}
});

In this link, you can access the complete code for Class.create() in the Github repository.