ES6

Question 1

What is a code block? What are some examples of a code block?

Answer 1

where code is executed, usually inside curly brackets

Question 2

What does block scope mean?

Answer 2

global or local, where a variable is accessible. if inside a code block and using let: the block scope is local. If outside of code block or var is used then block scope is global

let and const variables are only accessible inside the code block

Question 3

What is the scope of a variable declared with const or let?

Answer 3

block-scope, can only be accessed inside the code block if inside a code block

Question 4

What is the difference between let and const?

Answer 4

let: is mutable–> can be changed and mutated within the scope
const: is immutable –> cannot be changed or reassigned, but can add inside

Question 5

Why is it possible to .push() a new value into a const variable that points to an Array?

Answer 5

when pushing, you are not reassigning or redeclaring, you are adding to the object so techincally not really “changing” anything

Question 6

How should you decide on which type of declaration to use?

Answer 6

when variable is not going to be reassigned use const, when it is, then use let

if read only use const

Question 7

how can you change const variable

Answer 7

you can change const property values but not change the object literal

obj = {a: 2}
obj.a = 3  

not

obj = {a: 2}
obj = {a : 3}

you can also add (push) to const array

Question 8

What is the syntax for writing a template literal?

Answer 8

back ticks –> some string
white spaces count
can do new line

Question 9

What is “string interpolation”?

Answer 9

adding variable within template literal –>

const name = 'bob'
`my name is ${name}`

Question 10

What is destructuring, conceptually?

Answer 10

assigning variables in regards to an object/ array structure
assigning it in a ‘backwards’ way

Question 11

What is the syntax for Object destructuring?

Answer 11

{property1: var1, property2: var2} = object

if var is same name as property name –>
{var1, var2} = obj

Question 12

What is the syntax for Array destructuring?

Answer 12

[var1, var2, var3] = array

to get leftovers –>
[var1, var2, …leftovers] = array

to skip through first values –>
[, , , var] = array

Question 13

How can you tell the difference between destructuring and creating Object/Array literals?

Answer 13

the variables are within an object bracket or array bracket and the assignment value is the object/array you are pulling value from

Question 14

deconstructing objects with null returns from func

deconstructing array with null returns from fun

Answer 14

use OR operator and empty object as falback –>

let { firstName, lastName } = getPerson() || {};

let [a = 10, b = 20] = getItems() || [];

Question 15

setting default values for array deconstruction

Answer 15

assign value within deconstructor

let [, , thirdItem = 0] = getItems();

Question 16

What is the syntax for defining an arrow function?

Answer 16

const varName = (parameter) => { codeblock }

Question 17

When an arrow function’s body is left without curly braces, what changes in its functionality?

Answer 17

right side must have return expression, if statement on right side, must put it inside curly braces

Question 18

How is the value of this determined within an arrow function?

Answer 18

value of [this] is determined when arrow function is defined

this becomes outside of scope but within function

since arrow function [this] is defined in definition time, when not inside a function, this in an arrow function becomes window

Question 19

What are the three states a Promise can be in?
How do you handle the fulfillment of a Promise?
How do you handle the rejection of a Promise?

Answer 19

pending, fulfilled, rejected

fulfillment of a promise is with .then( ) and whatever you want to happen

rejection of a promise is with .catch( ) or also.then( )

Question 20

What is Array.prototype.filter useful for?

Answer 20

to apply a call back function to each element of an array
returns a new array that applies to the condition of individal arrays

in the call back return has to be true or false to decide if it will be returned in the output array

Question 21

What is Array.prototype.map useful for?

Answer 21

to apply a callback function to each element of an array

Question 22

What is Array.prototype.reduce useful for?

Answer 22

to stack array values into one value

Question 23

What is “syntactic sugar”?

What is “refactoring”?

Answer 23

syntactic sugar is when you make a syntax “sweeter” to make things easier to read or express

refactoring is restructuring code without changing its functionality to make it easier to build onto or to read/understand

Question 24

What is the typeof an ES6 class?
Describe ES6 class syntax.

Answer 24

object,

class NameOfClass {

constructor(parameters) {

}

methods( ) {

} 

}