Intermediate JavaScript

Question 1

What is the DOM

Answer 1

Document Object Model

Question 2

What is the Virtual DOM?

Answer 2

A virtual DOM is a lightweight JavaScript representation of the DOM used in declarative web frameworks such as React, Vue.js, and Elm. Updating the virtual DOM is comparatively faster than updating the actual DOM.

Question 3

Window Object

Answer 3

Represents the browser window

Question 4

Document Object

Answer 4

Represents the web page

Question 5

Image Object

Answer 5

Represents an HTML IMG tag

Question 6

History Object

Answer 6

Contains browser history

Question 7

Navigator Object

Answer 7

Contains niformation about the visitor’s browser

Question 8

All global JS objects, functions and variables automatically become….

Answer 8

members of the window object

Question 9

Global variables (Window object) are…

Answer 9

properties of the window object

Question 10

Global functions (window object) are..

Answer 10

methods of the window object

Question 11

Some methods of the Window Object

Answer 11

window. open
window. close
window. moveTo
window. resizeTo

Question 12

Finding HTML (Document Object), few examples

Answer 12

getElementsById
getElementsByTagName
getElementsByClassName

Question 13

Changing HTML (Document Object)

Answer 13

element. innerHTML =
element. attribute =
element. setAttribute (attribute,value)

Question 14

Adding or Deleting Elements (Document Object)

Answer 14

document. createElement(element)
document. removeChild(element)
document. appendChild(element)

Question 15

Event Handler (Document Object)

Answer 15

document.getElementById(id).onclick = function () {code}

Question 16

Create an Image Object

Answer 16

const x = document.createElement(“IMG”)

Question 17

Some Image Object properties

Answer 17

complete
naturalHeigth
naturalWidth
src

Question 18

Image rollover?

Answer 18

Two images. Change onMouseOver and onMouseOut

Question 19

Return the anchor part of a URL (Location Object)

Answer 19

var x = location.hash;

Question 20

Which Methods are there for the Location Object?

Answer 20

assign() Loads a new document
reload() Reloads the current document
replace() Replaces the current document with a new one

Question 21

Difference between replace or assign (location object)

Answer 21

After using replace the current page will not be saved in the session history

Question 22

Which Navigator propertie returns the version of the browser?

Answer 22

appVersion

Question 23

Which Navigator object returns the operating system?

Answer 23

platform

Question 24

Which Navigator property returns the name of the browser?

Answer 24

appName

Question 25

Which three methods to extract a part of String are there?

Answer 25

slice(start, end) substring(start, end) substr(start, length)

Question 26

What does slice()? (String)

Answer 26

extracts a part of a string and returns the extracted part in a new string.

Question 27

What doest the substring() method?

Answer 27

substring() is similar to slice(). | The difference is that substring() cannot accept negative indexes.

Question 28

What does the substr() method?

Answer 28

substr() is similar to slice(). | The difference is that the second parameter specifies the length of the extracted part.

Question 29

Difference between indexOf() and search() method?

Answer 29

``` The search() method cannot take a second start position argument. The indexOf() method cannot take powerful search values (regular expressions). ```

Question 30

String.match....

Answer 30

The match() method searches a string for a match against a regular expression, and returns the matches, as an Array object.

Question 31

What is a regular expression? Regexp

Answer 31

A regular expression is a sequence of characters that forms a search pattern. The search pattern can be used for text search and text replace operations.

Question 32

In JavaScript, regular expressions are often used with the two string methods: search() and replace().

Answer 32

The search() method uses an expression to search for a match, and returns the position of the match. The replace() method returns a modified string where the pattern is replaced.

Question 33

Regular Expression Patterns

Answer 33

Brackets are used to find a range of characters: Expression [abc] Find any of the characters between the brackets [0-9] Find any of the digits between the brackets (x|y) Find any of the alternatives separated with | Metacharacters are characters with a special meaning: Metacharacter \d Find a digit \s Find a whitespace character \b Find a match at the beginning of a word like this: \bWORD, or at the end of a word like this: WORD\b \uxxxx Find the Unicode character specified by the hexadecimal number xxxx

Question 34

RegExp Object

Answer 34

In JavaScript, the RegExp object is a regular expression object with predefined properties and methods.

Question 35

Reg Exp Object methods

Answer 35

exec() Tests for a match in a string. Returns the first match test() Tests for a match in a string. Returns true or false toString() Returns the string value of the regular expression

Question 36

What type of error is most likely to debug using watchpoints?

Answer 36

Logical

Question 37

What is a typical watchpoint in JS?

Answer 37

alert()

Question 38

What type of error after script has loaded?

Answer 38

Run-time

Question 39

What are run time erros typically caused by?

Answer 39

Improper use of commands

Question 40

Syntax-error

Answer 40

Load time (also called compiler / interpreter error)

Question 41

What to use to repeat a group of statement fora particular range of values?

Answer 41

For loop

Question 42

Control structures...

Answer 42

Make decisions based on Boolean values

Question 43

Substitute for the neste if..else statement?

Answer 43

Switch

Question 44

Purpose of the switch statement?

Answer 44

To compare a value against another to search for a match

Question 45

Purpose of the break statement?

Answer 45

To exit a control structure

Question 46

Continue statement..

Answer 46

Force the flow of control back to the top of the loop

Question 47

How to check if Java is enabled?

Answer 47

Use javaEnabled() method (navigator object)

Question 48

Limitation of virtual DOM?

Answer 48

Changes aren't directly reflected on the webpage

Question 49

The history object has one property....

Answer 49

length

Question 50

What is the JS equivalent fo the browser's back button?

Answer 50

history.go(-1);

Question 51

What is the default object in JS?

Answer 51

Window

Question 52

How to bring a window object to the top?

Answer 52

window.moveTo()

Question 53

Create a new history entry?

Answer 53

pushstate()

Question 54

Diffing =

Answer 54

comparing the new virtual DOM with previous version

Question 55

window.open() method uses 3 segments

Answer 55

URL, window name and list of window

Question 56

Comma delimited list from array

Answer 56

Use myArray.join(",");

Question 57

Declare a regular expression:

Answer 57

var ex = /Ron/;

Question 58

Difference between shift and pop

Answer 58

shift removes and returns the first element, pop the last element

Question 59

How to extract username from var email = ron@outlook.com

Answer 59

email.substring(0, email.indexOf("@") 0 = starting index @ = starting index --> up to (in this case @ )

Question 60

To use any Data or Time you must create a new instance or copy

Answer 60

var mydate = new Date();

Question 61

How to repeat a method or command after x-time

Answer 61

setTimeOut() | function.setTimeOut(time);

Question 62

The join() method, by default, uses the....

Answer 62

comma seperator

Question 63

Why use regular expression instead of string for matching?

Answer 63

regular expression can match a large number of strings

Question 64

Math.random returns...

Answer 64

any value in range 0 - 1 with 0 included and 1 excluded

Question 65

getDate() returns...

Answer 65

The date number (17 if it's 17th of november)

Question 66

Regex, string, Math, Array, Date are....

Answer 66

language objects

Question 67

String length is...

Answer 67

string.length (NOT a method so no brackets)

Question 68

floor, ceil, sin are...

Answer 68

Math objects

Question 69

substr() method takes two parameters...

Answer 69

1. Starting index | 2. Number of characters to extract

Question 70

charAt() example..

Answer 70

firstName.charAt(4);

Question 71

What is a JS class?

Answer 71

``` A JavaScript class is not an object. It is a template for JavaScript objects. ```

Question 72

THe prototype is available in ...... JS object

Answer 72

every

Question 73

Inheritance =

Answer 73

class-based and prototype based

Question 74

Yield operator

Answer 74

Pause or resume a generator function

Question 75

Add additional fields to custom object...

Answer 75

Use prototype

Question 76

Which object can access items in a collection?

Answer 76

Iterator

Question 77

Call the functions on a paretn object?

Answer 77

Use the super keyword