Javascript

Question 1

Javascript supports what type of style?

Answer 1

object-oriented, functional, and event driven

Question 2

How is JavaScript executed client-side?

Answer 2

Each browser has a JavaScript engine that || !interprets! || the code

Question 3

Internal definition

Answer 3

-JS in HTML file
-Imbedded in script tags
-In head or body
-Executed once parsed

 window.alert("Test");

Question 4

External definition

Answer 4

• Script in a .js file
• Script tags
• In header or body
• Executed once parsed

Question 5

Javascript types

Answer 5

Primitive:
-number
-string
-boolean
-undefined
Complex
-object (inc arrays)
-function

type can be checked with typeof(var);

Question 6

What does JSON stand for?

Answer 6

JavaScript Object Notation

Question 7

Conversion between JSON and JavaScript

Answer 7

var obj = {name: “Grischa”, age: 31}; //Object

var json = JSON.stringify(obj); //JSON

var json = ‘{“name”: “Grischa”, “age”: “31”}’; //JSON String

var obj = JSON.parse(json); //Object

JSON.stringify() removes functions

Question 8

Parts of the bad rep of JS covered in VEFF1

Answer 8

Type conversion
Comparators
Scope
Hoisting

Question 9

JS type conversion

Answer 9

Types are dynamic

Type conversion is from left to right.

var m = 5 + 6 + '5';
m = '115'

Question 10

JS Comparison

Answer 10

== compares the value, so it does type conversion (!=)

=== compares both the type and value (!==)

Question 11

JS Scopes

Answer 11

Global, local, and block scope

global/local scope
var x = 'bla'

Question 12

JS Hoisting

Answer 12

JS “hoists” (moves) variable declarations to the top of the scope

Question 13

JS Calback

Answer 13

Used to execute functionality after work is done.

Callback function is provided as a function parameter

Callback function is caled when main function is finished.

Question 14

Why use Callback functions

Answer 14

Good tool to use when dealing with the internet, you fx dont know how long an HTTP response takes. No need to check for results. You can continue doing stuff while you wait for the callback function!

Question 15

AJAX (Asynchronous JavaScript And XML) why and what?

Answer 15

BTW it allows more than just XML, inc JSON.

Allows HTTP requests and responses after the page has been loaded.

Update the page without reload

Load only what is needed

Load different data depending on user actions

Use the standard XMLHttpRequest object to make requests.

Question 16

Axios: why and what?

Answer 16

JS library used to symplify HTTP requests