JavaScript

Question 1

What is a method?

Answer 1

Function stored as a value in an object

Question 2

How can you tell the difference between a method definition and a method call?

Answer 2

Method definition is very similar to a function definition (no arguments being passed) while a method call would be the object.methodname(argument).

Question 3

Describe method definition syntax (structure).

Answer 3

Function definition being assigned to a property of an object

Question 4

Describe method call syntax (structure).

Answer 4

object.methodname(argument)

Question 5

How is a method different from any other function?

Answer 5

Method is associated as an object while functions are independent.

Question 6

What is the defining characteristic of Object-Oriented Programming?

Answer 6

Object can contain both data and methods (behavior)

Question 7

What are the four “principles” of Object-Oriented Programming?

Answer 7

Inheritance, Polymorphism, Abstraction, Encapsulation

Question 8

What is “abstraction”?

Answer 8

Taking complex problems and making it accessible. The best example is a light switch. There’s a lot that happens under the hood but to humans you just flick a switch.

Question 9

What does API stand for?

Answer 9

Application Programming Interface

Question 10

What is the purpose of an API?

Answer 10

Allows your products and services to communicate with other products and services without having to constantly build new connectivity infrastructure.

Question 11

What is this in JavaScript?

Answer 11

Keyword referring to a variable that holds a value in an object you are working with

Question 12

What does it mean to say that this is an “implicit parameter”?

Answer 12

It is available in a function’s code block even though it was never included in the function’s parameter list or declared with var

Question 13

When is the value of this determined in a function; call time or definition time?

Answer 13

Call time. It technically does not have a value until the function is called.

Question 14

What does this refer to in the following code snippet?
var character = {
  firstName: 'Mario',
  greet: function () {
    var message = 'It\'s-a-me, ' + this.firstName + '!';
    console.log(message);
  }
};

Answer 14

Nothing it has not been invoked yet

Question 15

Given the character object, what is the result of the following code snippet (character.greet())? Why?
var character = {
  firstName: 'Mario',
  greet: function () {
    var message = 'It\'s-a-me, ' + this.firstName + '!';
    console.log(message);
  }
};
character.greet();

Answer 15

You will get the message because it retrieves the object with the property value

Question 16

Given the character object, what is the result of the following code snippet *var hello = character.greet; hello()? Why?
var character = {
  firstName: 'Mario',
  greet: function () {
    var message = 'It\'s-a-me, ' + this.firstName + '!';
    console.log(message);
  }
};
var hello = character.greet;
hello();

Answer 16

Undefined

Question 17

How can you tell what the value of this will be for a particular function or method definition?

Answer 17

You can’t

Question 18

How can you tell what the value of this is for a particular function or method call?

Answer 18

If there is a . it is always what is to the left of it

Question 19

What kind of inheritance does the JavaScript programming language use?

Answer 19

Prototypal Inheritance

Question 20

What is a prototype in JavaScript?

Answer 20

Object that a bunch of objects can build off of

Question 21

How is it possible to call methods on strings, arrays, and numbers even though those methods don’t actually exist on objects, arrays, and numbers?

Answer 21

From prototypes

Question 22

If an object does not have it’s own property or method by a given key, where does JavaScript look for it?

Answer 22

On the prototype

Question 23

What does the new operator do?

Answer 23

1. Creates a blank, plain JavaScript Object
2. Adds a property to the new object (__proto__) that links to the constructor functions prototype
3. Binds newly created object instances as ‘this’ context
4. Returns this if the function doesn’t return an object

Question 24

What property of JavaScript functions can store shared behavior for instances created with new?

Answer 24

Prototype Property

Question 25

What does the instanceof operator do?

Answer 25

Tests to see if prototype property of a constructor appears in the prototype chain. Returns a boolean