JSFiddle - React, Tailwind, and code Playground

JavaScript

PrependableObject = function(obj){
    this.obj = obj;
}

PrependableObject.prototype.prepend = function(key, val){
    
    var newObj  = new Object(),
        oldKeys = Object.keys(this.obj);
    
    newObj[key] = val;
    
    for (var i=0; i< oldKeys.length; i++){
    
        newObj[oldKeys[i]] = this.obj[oldKeys[i]];
    }
    
    return newObj;

}

function getCarData() {
    return [
      {car: "Mercedes A 160", year: 2006, available: true, comesInBlack: 'yes'},
      {car: "Citroen C4 Coupe", year: 2008, available: false, comesInBlack: 'yes'},
      {car: "Audi A4 Avant", year: 2011, available: true, comesInBlack: 'no'},
      {car: "Opel Astra", year: 2004, available: false, comesInBlack: 'yes'},
      {car: "BMW 320i Coupe", year: 2011, available: false, comesInBlack: 'no'}
    ];
 }

var carData = getCarData();

carData.forEach(function(obj, index){
    
    var obj = new PrependableObject(obj),
        newObj = obj.prepend('check', false);
    
    carData[index] = newObj;
});

var car1 = carData[0];

Object.keys(car1).forEach(function(key, i){
    
    console.log(key + ' = ' + car1[key]);

})