Useful methods when working with inheritance

hasOwnProperty

Object.hasOwnProperty('nameOfProperty') - always make sure the name of the property is in quotes. Classes that inherit from other classes will also return true if the property is checked.

Example 1

var taco = {
  food: 'taco'
}

taco.hasOwnProperty(food); // returns an error
taco.hasOwnProperty('food'); // returns true

Example 2 with inheritance

function Person(name) {
  this.name = name
}

Person.prototype.greet = function() {
  return 'Hello, my name is ' + this.name;
};

function Student(name, course) {
  Person.call(this, name);
  this.course = course;
}

Student.prototype = Object.create(Person.prototype);
Student.prototype.constructor = Student;

var person = new Person('Bob');
var student = new Student('Tom', 'WDI');

person.hasOwnProperty('name'); //returns true
student.hasOwnProperty('course'); //returns true
student.hasOwnProperty('name'); //returns true

instanceof

This method is a bit more common, and the syntax looks like this:

object instanceof Class

Example 1:

var color1 = {};
color1 instanceof Object; // returns true

Example 2 with inheritance

function Person(name) {
  this.name = name
}

Person.prototype.greet = function() {
  return 'Hello, my name is ' + this.name;
};

function Student(name, course) {
  Person.call(this, name);
  this.course = course;
}

Student.prototype = Object.create(Person.prototype);
Student.prototype.constructor = Student;

var p = new Person('Bob');
var s = new Student('Tom', 'WDI');

s instanceof Person //returns true
p instanceof Student //returns false
Person instanceof Object //returns true
String instanceof Object //returns true
Object instanceof Boolean //returns false

isPrototypeOf

This method is used a bit less frequently, but the syntax looks like this:

Object.prototype.isPrototypeOf(objectInstance);

Example:

var p = new Person('Bob');
var s = new Student('Tom', 'WDI');

Person.prototype.isPrototypeOf(s); // returns true
Student.prototype.isPrototypeOf(p); // returns false

You can read more about the difference between isPrototypeOf and isInstanceOf here