JSFiddle - React, Tailwind, and code Playground

JavaScript

function User(fullName) {
    this.fullName = fullName;
    Object.defineProperties(this, {
        'firstName': {
            get() {
                let split = this.fullName.split(' ');
                this.firstName = split[0];
            }
        },
        'lastName': {
            get() {
                let split = this.fullName.split(' ');
                this.lastName = split[1];
            }
        }
    })
};

var vasya = new User("Василий Попкин");
console.log(vasya.firstName); //undefined
console.log(vasya.lastName); //undefined