function Fish(habitat, length) {
  this.habitat = habitat;
  this.length = length;
}

Fish.prototype.renderProperties = function(element) {
  element.innerHTML = JSON.stringify(this)
};

function Trout(habitat, length, variety) {
  this._super.call(this, habitat, length);
  this.variety = variety;
}

Trout.prototype = Object.create(Fish.prototype);
Trout.prototype.constructor = Trout;
Trout.prototype._super = Fish;

Trout.prototype.renderPropertiesWithSuper = function(element) {
  element.className="green"; 
  this.renderProperties(element);
};

let grouper = new Fish("saltwater", "26in");
grouper.renderProperties(document.getElementById("grouper"));

var rainbowTrout = new Trout("freshwater", "14in", "rainbow");
//invoke function from parent
rainbowTrout.renderProperties(document.getElementById("rainbowTrout"));
//invoke function from child
rainbowTrout.renderPropertiesWithSuper(document.getElementById("rainbowTroutParent"));