Why pass the second argument an object reference?

Hello! Read the documentation Knockaut.js. It is not quite clear in one of the examples why you pass a reference to himself. Here's an example:

<div class="log" data-bind="text: computedLog"></div>
<!--ko if: step() == 0-->
 <p>First name: <input data-bind="textInput: firstName"></p>
<!--ko if: step() == 1-->
 <p>Last name: <input data-bind="textInput: lastName"></p>
<!--ko if: step() == 2-->
 the <div>Prefix: <select data-bind="value: prefix, options: ['Mr.', 'Ms.','Mrs.','Dr.']"></select></div>
 <h2>Hello, <span data-bind="text: fullName"> </span>!</h2>
<p><button type="button" data-bind="click: next">next</button></p>

The view model:
function AppData() {
 this.firstName = ko.observable('John');
 this.lastName = ko.observable('Burns');
 this.prefix = ko.observable('Dr.');
 this.computedLog = ko.observable('Log: ');
 this.fullName = ko.pureComputed(function () {
 var value = this.prefix() + "" + this.firstName() + "" + this.lastName();
 // Normally, you should avoid writing to observables within a computed pure 
 // observable (avoiding side effects). But this example is meant to demonstrate 
 // its internal workings, and writing a log is a good way to do so.
 this.computedLog(this.computedLog.peek() + value + '; ');
 return value;
 }, this);
ko.applyBindings(new AppData());

PureComputed method accepts as second parameter a reference to the constructor AppData. Why?
July 9th 19 at 13:22
1 answer
July 9th 19 at 13:24
Not a constructor, and the instance, if that. Because if pureComputed required to work in a particular context, it is necessary in this context to convey, otherwise where will this.prefix, this.firstName and so on.

By the way, I learned that in three minutes reading the documentation of knockout, never seen before.
What is meant by "instance"? - Sam_Reynolds commented on July 9th 19 at 13:27
function AppData() {} // AppData designer aka class 
new var appData = new AppData() // appData — aka the instance of instance
- genevieve_Upton commented on July 9th 19 at 13:30
Thank you. - Sam_Reynolds commented on July 9th 19 at 13:33

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