JSFiddle - React, Tailwind, and code Playground

JavaScript

var a = function(){
    var instance, A, updateLength;

    instance = this;
    A = [];
    this.length = 0;

    updateLength = function()
    {
      instance.length = A.length;
    }

    this.add = function(x){
        A.push(x);
        updateLength();
    };
    this.remove = function(){
        var popped = A.pop();
        updateLength();

        return popped;
    };
};


var x = new a();
x.add(1);
x.add(2);
x.add(3);
x.add(4);
alert("x.len :: " + x.length); // 2
alert("CurrItem :: " + x.remove()); // 4
alert("x.len :: " + x.length); // 1
alert("CurrItem :: " + x.remove()); // 3
alert("x.len :: " + x.length); // 1