Object.prototype.toString()

function Dog(name) {
  this.name = name;
}

const dog1 = new Dog("Gabby");

Dog.prototype.toString = function dogToString() {
  return `${this.name}`;
};

console.log(dog1.toString());
// Expected output: "Gabby"

toString();

const arr = [1, 2, 3];

arr.toString(); // "1,2,3"
Object.prototype.toString.call(arr); // "[object Array]"

function Dog(name, breed, color, sex) {
  this.name = name;
  this.breed = breed;
  this.color = color;
  this.sex = sex;
}

theDog = new Dog("Gabby", "Lab", "chocolate", "female");

theDog.toString(); // returns [object Object]

Dog.prototype.toString = function dogToString() {
  var ret =
    "Dog " +
    this.name +
    " is a " +
    this.sex +
    " " +
    this.color +
    " " +
    this.breed;
  return ret;
};

"Dog Gabby is a female chocolate Lab";

var toString = Object.prototype.toString;

toString.call(new Date()); // [object Date]
toString.call(new String()); // [object String]
toString.call(Math); // [object Math]

// Since JavaScript 1.8.5
toString.call(undefined); // [object Undefined]
toString.call(null); // [object Null]