JavaScript ES6

Question 1

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

Answer 1

Stuff between curly braces. Functions, loops, conditionals.

Question 2

What does block scope mean?

Answer 2

anything declared inside a codeblock, stays inside the codeblock.

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

you can reassign a let variable but not a const variable.

Question 5

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

Answer 5

the array values can be changed, but the variable cannot be reassigned.

Question 6

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

Answer 6

If you are sure you will not need to reassign a variable, use const, otherwise use let. If you are unsure, use const, and change it later if you find out you do need to reassign it.

Question 7

What is the syntax for writing a template literal?

Answer 7

Using backticks and ${EXPRESSION}

Question 8

What is “string interpolation”?

Answer 8

writing strings with substitutions.

Question 9

What is destructuring, conceptually?

Answer 9

unpacking values from arrays, or properties from objects, into distinct variables.

Question 10

What is the syntax for Object destructuring?

Answer 10

const { objProperty: newVariable, objProperty: newVariable, objProperty: newVariable, etc } = obj;

Question 11

What is the syntax for Array destructuring?

Answer 11

const [newVariable, newVariable, newVariable, etc] = array;

Question 12

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

Answer 12

The brackets or curly braces come before the assignment operator.

Question 13

What is the syntax for defining an arrow function?

Answer 13

let functionName = (params) => { code block };

Question 14

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

Answer 14

it will return the expression after the =>

Question 15

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

Question 16

What are the three states a 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

.then

Question 18

How do you handle the rejection of a Promise?

Answer 18

.catch

Question 19

What does Array.filter do?

Question 20

What should the callback function return?

Answer 20

returns a truthy or falsey value and if its truthy, add it to the copy.

Question 21

What is Array.filter useful for?

Question 22

What does Array.map do?

Question 23

What should the callback function return?

Question 24

What is Array.filter useful for?

Question 25

What does Array.reduce do?

Answer 25

walks through an array and reduces it into a single value.

Question 26

What action should the callback function perform?

Answer 26

examine the current element, do a computation to it and add it to the accumulated value.

Question 27

What should the callback function return?

Question 28

What is Array.reduce useful for?

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. Classes in JS are built on prototypes but also have some syntax and semantics that are unique to classes.

Question 30

When would you want to use a class?

Answer 30

If you have data or functionality to encapsulate.

Question 31

How do you declare a class?

Answer 31

using the class keyword
class NameOfClass {
code block
}

Question 32

How do you inherit from another class?

Answer 32

using the extends keyword
class NameOfClass extends SuperClass {
code block
}

Question 33

Why would you want to inherit from another class?

Answer 33

reuse, extend, and modify the behavior defined in other classes

Question 34

How do you add methods and properties to a class?