JavaScript ES6

Question 1

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

Answer 1

block of code inside curly braces

Question 2

What does block scope mean?

Answer 2

only accessible inside the block

Question 3

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

Answer 3

block scoped variables

Question 4

What is the difference between let and const?

Answer 4

const = x change
let = can change

Question 5

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

Answer 5

not reassigning it, just changing its value

Question 6

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

Answer 6

if reassignment is needed use let /
otherwise use const

Question 7

What is the syntax for writing a template literal?

Answer 7

using backticks ` `

Question 8

What is “string interpolation”?

Answer 8

the ability to substitute part of the string for the values of variables or expressions.

Question 9

What is destructuring, conceptually?

Answer 9

taking properties of object out and assigning them to variables

Question 10

What is the syntax for Object destructuring?

Answer 10

const book1 = { title: ‘Goodnight Punpun’, author: ‘Inio Asano’, libraryID: 3353 };

const { title, author, libraryID } = book1;

Question 11

What is the syntax for Array destructuring?

Answer 11

const [x, y, z] = library;

Question 12

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

Answer 12

creating : variable left hand side

destructuring: variable right hand side

Question 13

What is the syntax for defining an arrow function?

Answer 13

parameters => expression/return statement

Question 14

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

Answer 14

returns the result of the expression

Question 15

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

Answer 15

Unlike an anonymous function, an arrow function captures the this value of the enclosing context instead of creating its own this context.

Question 16

const bar = (n) => 2 * n

Answer 16

same as
function bar (n) {
return 2 * n
};

Question 17

What are the three states a Promise can be in?

Answer 17

pending: initial state, neither fulfilled nor rejected.

fulfilled: meaning that the operation was completed successfully.

rejected: meaning that the operation failed.

Question 18

How do you handle the fulfillment of a Promise?

Answer 18

.then()

Question 19

How do you handle the rejection of a Promise?

Answer 19

.catch()

Question 20

What is “syntactic sugar”?

Answer 20

Designed to make things easier to read or to express. It makes the language “sweeter” for human use: things can be expressed more clearly, more concisely, or in an alternative style that some may prefer.

Question 21

What is the typeof an ES6 class?

Answer 21

Object

Question 22

Describe ES6 class syntax.

Answer 22

class Person {
constructor(name) {
this.name = name;
}
getName() {
return this.name;
}
}

Question 23

What is “refactoring”?

Answer 23

restructuring the format to make it more readable