Object-Oriented Programming

Question 1

What is a method?

Answer 1

a method is a function which is a property of an object

Question 2

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

Answer 2

method call does not have a code block

Question 3

Describe method definition syntax (structure).

Answer 3

method: function( ) { }

Question 4

Describe method call syntax (structure).

Answer 4

Object.method( )

Question 5

How is a method different from any other function?

Answer 5

method is associated with object, function is not

Question 6

What is the defining characteristic of Object-Oriented Programming?

Answer 6

objects can contain both data (as properties) and behavior (as methods)

Question 7

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

Answer 7

abstraction, encapsulation, inheritance, polymorphism

Question 8

What is “abstraction”?

Answer 8

simplifying complex behavior

Question 9

What does API stand for?

Answer 9

application programming interface

Question 10

What is the purpose of an API?

Answer 10

connects computers and programs to each other

Question 11

What is ‘this’ in JavaScript?

Answer 11

implicit parameter of all JavaScript functions

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

Question 13

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

Answer 13

call

Question 14

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

Answer 14

you can’t

Question 15

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

Answer 15

the object to the left of the dot

Question 16

What kind of inheritance does the JavaScript programming language use?

Answer 16

prototype-based or prototypal

Question 17

What is a prototype in JavaScript?

Answer 17

the mechanism by which JavaScript objects inherit features from one another

Question 18

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 18

they come with built in prototype objects

Question 19

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

Answer 19

on the prototypes

Question 20

What does the new operator do?

Answer 20

• create an instance of a user-defined object type
• adds a property to the new object (__proto__) that links to the constructor function’s prototype object
• binds the newly created object instance as the this context
• returns this if the function doesn’t return an object

Question 21

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

Answer 21

prototype

Question 22

What does the instanceof operator do?

Answer 22

tests to see if the prototype property of a constructor appears anywhere in the prototype chain of an object. The return value is a boolean value.