W3. The DOM

Question 1

How does parameter passing work in JS for base types and object types?

Answer 1

Base types (String, Number,  Boolean) passed by value.
Object types (Object, Function, Array) passed by reference.
(Parameters are un-typed)

Question 2

What does DOM stand for?

Answer 2

Document Object Model

Question 3

In the DOM, what does the Window object refer to?

Answer 3

• The OS window hosting the page
• global object in JS program when it is executed in a browser
• contains other objects including document, navigator and screen and references to other windows and frames

Question 4

In the DOM, what does the Navigator object refer to?

Answer 4

Browser application in use
Includes: 
- name of browser
- platform (e.g MacIntel)
- language of browser (e.g. english)
- if browser is online
- geolocation
- cookie info

Question 5

In the DOM, what does the Screen object refer to?

Answer 5

Physical monitor in use
Properties:
- width 
- height
- colourDepth
- pixelDepth etc.

Question 6

In the DOM, what does the Document object refer to?

Answer 6

• currently displayed HTML
• root of the DOM tree (parent of tag)
• always directly accessible via JS
  (lots of methods e.g. getElementById)

Question 7

In the DOM, what does the Node class refer to?

Answer 7

Class that most objects in DOM inherit from
Properties:
- childNodes
- firstChild
- lastChild
- nextSibling
- parentNode etc.

Question 8

What does JSON stand for?

Answer 8

JavaScript Object Notation

Question 9

What is JSON used for?

Answer 9

• syntax for storing and exchanging data
• text, written with JS object notation
• easy conversion from/to JS objects
• can be sent between browser and server

Question 10

What 2 methods are there for converting between JSON and JS?

Answer 10

.stringify - to convert to a JSON string

.parse - to convert to a JS object

Question 11

What is a WebSocket?

Answer 11

• provides (full-duplex) communication over a TCP connection between web browser and web server
  (data moves in both directions)

Question 12

How do WebSockets allow two-way communication between client and server?

Answer 12

• have a standardised way of allowing the server to send content to the client without it first being requested by client

Question 13

List 4 WebSocket events

Answer 13

• on open
• on error
• on close
• on message