items = [{"Id":"car","color":"blue"},{"Id":"truck","color":"red"}]

newItem = {"Id":"car","color":"yellow"}

items = [{"Id":"car","color":"yellow"},{"Id":"truck","color":"red"}]

for (var i=0; i<items.length; i++)
{
            var x = items[i];

            if(x.Id == newItem.Id){    //first check if id matches
                if (JSON.stringify(items[i]) == JSON.stringify(newItem))  {
                    alert('objects are same');
                    return ;
                }
                else {
                    var newColor = JSON.stringify(x).replace(x.color, newItem.color);
                    alert(JSON.parse(newColor));

                }
            }
}