Js

Question 1

Var declaration

Answer 1

var’s declaration is hoisted not value

Question 2

== vs ===

Answer 2

== value

=== value and type

Question 3

Const

Answer 3

No reassignment of value

Question 4

Window.

Answer 4

Base global object

Question 5

I frame

Answer 5

Window on window

Access through window.frames

Question 6

Document.

Answer 6

HTML that is loaded on the window

Question 7

Undefined

Answer 7

Var has no value. JS sets the value to undefined

Question 8

Prototype inheritance

Answer 8

Object -> property

Array.prototype.newMethod = ()=>

Question 9

Function declaration vs expression

Answer 9

Declarations are hoisted

Expressions take variable scope

Question 10

Promises

Answer 10

Set up an a sync data retrevial

Question 11

shouldComponentUpdate

Answer 11

Triggered from external changes

Returns true or false
Args - (nextProps, nextState)

Question 12

Using ref

Answer 12

Ref={input => this.inputElement = input}

componentDidMount() {
if (this.props.position ===0) {
this.inputElement.focus() }

Question 13

shouldComponetUpdate

Answer 13

shouldComponetUpdate(nextProps, nextState) {

return nextProps.persons !== this.pros.persons

Question 14

Redux

Answer 14

Global Store -> Reducer -> Action(mapDispatchToProps) -> Dispatch -> Component

Global Store -> Triggers -> Subscription -> Component

Question 15

Why is typeOf bar === ‘object’ not a good check?

Answer 15

Because null is also an object. Should be
typeOf bar === ‘object’ && bar !== null

If bar should be an array an ES5 check would be:
Array.isArray(bar)

Question 16

S in Solid

Answer 16

Single Responsibility Principle - class should have one and only one reason to change, meaning that a class should have one job

Question 17

O in Solid

Answer 17

Open Closed Principle - Objects should be open for extension, but closed for modification

Question 18

L in Solid

Answer 18

Liskov Substitution Principle - Every sub class should be substitutable for the super class

Question 19

I in Solid

Answer 19

Interface Segregation Principle - clients should be forced to depend on methods they do not use

Question 20

D in Solid

Answer 20

Dependency Inversion Principle - high level must not depend on low level they should depend on abstractions.

Question 21

Object.assign({}, {})

Answer 21

Clones object

ES6
{…state}

Question 22

Box Model

Answer 22

Wraps every HTML element (Margin, Border, Padding, Content)

Question 23

CSS Specitivity

Answer 23

Last In - First out
Class
ID
! Important

Question 24

.filter method
array = [1, 2, 3]
newArray = array.filter( i => i !==3)

What is returned

Answer 24

[1, 2]

Question 25

3 types React States

Answer 25

Local - show hide modal

Persistent - blog posts

Client - is auth