JSFiddle - React, Tailwind, and code Playground

JavaScript

function BaseClass() {
    var map = {};
    this.parseXML = function(key, value) {
        alert("BaseClass::parseXML()");
        map[key] = value;
    }
}

function ChildClass() {
    BaseClass.call(this);
    var parseXML = this.parseXML;
    this.parseXML = function(key, value, otherData) {
        alert("ChildClass()::parseXML()");
        parseXML.call(this, key, value);
    }
}

ChildClass.prototype = new BaseClass;

var a = new ChildClass();
a.parseXML();