ES6

Question 1

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

Answer 1

code blocks are denoted by curly braces { }
ex: if, for, while

Question 2

What does block scope mean?

Answer 2

the variable inside the block is a new variable and it shadows the variable declared at the top of the script

Question 3

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

Answer 3

block scoped

Question 4

What is the difference between let and const?

Answer 4

const - denotes that a variable is a constant and can’t be reassigned

let - can be reassigned

Question 5

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

Answer 5

the actual value to which the const variable reference is not immutable

Question 6

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

Answer 6

if the variable will be reassigned, use let

Question 7

What is the syntax for writing a template literal?

Answer 7

wrapping your text in backticks and writing expressions inside ${ }

Question 8

What is “string interpolation”?

Answer 8

replacing placeholders with values in a string literal

Question 9

What is destructuring, conceptually?

Answer 9

extracting data from arrays or objects into smaller parts

Question 10

What is the syntax for Object destructuring?

Answer 10

let / const keyword {
propertyOfObj: nameOfVariable
} = object

Question 11

What is the syntax for Array destructuring?

Answer 11

let / const keyword [varName1, varName2, etc] = array;

Question 12

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

Answer 12

creating - the name of the variable comes first
destructuring - curly brace / square bracket comes first

Question 13

What is the syntax for defining an arrow function?

Answer 13

(parameter) => {code block}

Question 14

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

Answer 14

without curly braces, it can only be a single expression (an implicit return), with curly braces, it needs a return keyword

Question 15

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

Answer 15

an arrow function doesn’t have it’s own this value and captures the this value of the lexical scope (the outer function)

Question 16

What are the three states a Promise can be in?

Answer 16

pending, fullfilled, rejected

Question 17

How do you handle the fulfillment of a Promise?

Answer 17

Promise.then() returns the message if available

Question 18

How do you handle the rejection of a Promise?

Answer 18

Promise.catch() returns an error method

Question 19

What is “syntactic sugar”?

Answer 19

syntax in a programming language for easier readability

Question 20

What is the typeof an ES6 class?

Answer 20

Function

Question 21

Describe ES6 class syntax.

Answer 21

class Name (capitalized) {
constructor(1, 2) {
this.1 = 1;
this.2 = 2;
}
}

Question 22

What is “refactoring”?

Answer 22

changing the design, structure, or implementation of code while keeping the functionality the same

Question 23

What must the return value of myFunction be if the following expression is possible?
myFunction()();

Answer 23

another function

Question 24

What does this code do?
const wrap = value => () => value;

Answer 24

it assigns the second arrow function to the const wrap

Question 25

In JavaScript, when is a function’s scope determined; when it is called or when it is defined?

Question 26

What allows JavaScript functions to “remember” values from their surroundings?

Answer 26

closures