ES6

Question 1

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

Answer 1

A block of code, examples being Functions, Objects and Array

Question 2

What does block scope mean?

Answer 2

Means the code inside is not accessible from outside the block. (What happens in the code block stays in the code block)

Question 3

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

Answer 3

Block Scope

Question 4

What is the difference between let and const?

Answer 4

let values can be reassigned,
while a const values are read only

Question 5

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

Answer 5

You are able to manipulate an array declared with const but you are unable to reassign it

Question 6

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

Answer 6

Depending if you want to read only or reassign the variable, if you don’t know ALWAYS use const first

Question 7

What is the syntax for writing a template literal?

Answer 7

Backsticks ( )
Newline (\n)
Newline continuation (\n)
Substitution ( ${expression} )

Question 8

What is “string interpolation”

Answer 8

A combination of a string and outputs inside the string

Question 9

What is restructuring, conceptually?

Answer 9

The breakdown of an array or object

Question 10

What is the syntax for Object destructuring?

Answer 10

const or let [ var, var, var… ] = Object

Question 11

What is the syntax for Array destructuring?

Answer 11

const or let {var, var, var… } = Array

Question 12

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

Answer 12

When creating an Object/Array the equal sign goes before the curly brace
When destructuring the equal sign goes after the curly brace

Question 13

What is the syntax of an arrow function?

Answer 13

() => expression

param => expression

(param) => expression

(param1, paramN) => expression

() => {
statements
}

param => {
statements
}

(param1, paramN) => {
statements
}

Question 14

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

Answer 14

becomes an expression rather than a statement

Question 15

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

Answer 15

Within an arrow function the this is not binded to the function

Question 16

What are the three states of Promise can be in?

Answer 16

Pending: initial state, neither fulfilled nor rejected

Fulfilled: meaning that the operation was completed successfully

Rejected: meaning that the operation failed

Question 17

How do you handle the fulfillment of a Promise?

Answer 17

With .then()

Question 18

How do you handle the rejection of a Promise?

Answer 18

With .catch()

Question 19

What does Array.filter do?

Answer 19

Creates a shallow copy of a portion of a given array, filtered down to just the elements from the given array that pass the test implemented by the provided function.

Question 20

What should the callback function return?

Answer 20

If value is true an array of matching values is returned

Question 21

What is Array.filter useful for?

Answer 21

To filter out unwanted/ wanted values

Question 22

What does Array.map do?

Answer 22

Creates a new array populated with the results of calling a provided function on every element in the calling array.

Question 23

What should the callback function return?

Answer 23

Returns a copy of an array with the given expression

Question 24

What is Array.map useful for?

Answer 24

To modify everything in an array without looping through it

Question 25

What does Array.reduce do?

Answer 25

Walks through an array and reduces it down to a single value

Question 26

What action should the callback function perform?

Answer 26

the action it performs is to examine the element, perform an expression and updates the accumulation

Question 27

What should the callback function return?

Answer 27

It should return the accumulated value

Question 28

What is Array.reduce useful for?

Answer 28

Useful for a few things

Question 29

What are JavaScript classes?

Answer 29

Classes are a template for creating objects. They encapsulate data with code to work on that data.

Question 30

When would you want to use a class?

Answer 30

When working with data

Question 31

How do you declare a class?

Answer 31

with the class keyword

Question 32

How do you inherit from another class?

Answer 32

class className extends extendedName {
super( )
}

Question 33

Why would you want to inherit from another class?

Answer 33

You want to be able to reuse the original without having it change it

Question 34

How do you add methods and properties to a class?