JSFiddle - React, Tailwind, and code Playground

JavaScript

function Huhn() {
    this.eier = 0;
}
Huhn.prototype.legeEi = function() {
    this.eier -= -1;
};

(function() {
    var alt = Huhn.prototype.legeEi;
    Huhn.prototype.legeEi = function() {
        alt.apply(this);
        alert(this.eier);
    };
})();

var myHuhn = new Huhn();
myHuhn.legeEi();