JS ES6

Question 1

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

Answer 1

A code block is the space between curly braces. Examples include the code block within function definitions. The code block of for loops and while loops.

Question 2

What does block scope mean?

Answer 2

Block scope begins at the first curly brace. Any variables defined, or reassigned within block scope are only accessible within that block scope.

Question 3

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

Answer 3

Their scope is block scope.

Question 4

What is the difference between let and const ?

Answer 4

let can be reassigned, const can not be. const is a read only reference. let doesn’t have to be initialized to a value when declared… const does.

Question 5

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

Answer 5

because a const variable is read-only… the actual value referenced isn’t immutable

Question 6

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

Answer 6

the declaration you use should be determined by whether or not a variable is intended to be reassigned or not

Question 7

What is the syntax for writing a template literal?

Answer 7

strings and/or variables written between backticks ( ` ` )

Question 8

What is string interpolation?

Answer 8

being able to substitute part of a string with values of variables or expressions

Question 9

What is destructuring, conceptually?

Answer 9

The mass assignment of object properties / array values to variables.

Question 10

What is the syntax for Object destructuring?

Answer 10

let { objProp1: var1, objProp2: var2 } = mainObj;

Question 11

What is the syntax for Array destructuring?

Answer 11

let [ var1, var2, var3 ] = exArray;

Question 12

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

Answer 12

the side on which the curly braces/square brackets are on

Question 13

What is the syntax for defining an arrow function ?

Answer 13

(p1,p2…) => {

}

Question 14

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

Answer 14

it becomes an implicit return value

Question 15

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

Answer 15

this isn’t defined when the arrow function is called, it’s inherited from the parent scope

Question 16

What are the three states a Promise can be in?

Answer 16

pending, fulfilled, and rejected

Question 17

How do you handle the fulfillment of a Promise?

Answer 17

you call the then() method of the Promise and pass whatever you would like done on the fulfillment

Question 18

How do you handle the rejection of a Promise?

Answer 18

you call the catch() method of the Promise and pass whatever you would like done on the fulfillment

Question 19

What is Array.prototype.filter useful for ?

Answer 19

it’s useful for locating and keeping values based off of some criteria that you provide. it’s a loop and conditional in one function

Question 20

What is Array.prototype.map useful for?

Answer 20

it’s useful for doing an expression on each index of an Array

Question 21

What is Array.prototype.reduce useful for?

Answer 21

combining the elements of an entire array into a single value

Question 22

What is syntactic sugar?

Answer 22

is syntax that is designed to make things easier to read or to express

Question 23

What is the typeof an ES6 class?

Answer 23

function

Question 24

Describe ES6 class syntax

Answer 24

keyword class and then the name you want your class to be capitalized

Question 25

What is refactoring?

Answer 25

the “cleaning up” of code without changing the functionality