ES6

Question 1

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

Answer 1

blocks are denoted by curly braces {} , for example, the if else, for, do while, while, try catch

Question 2

What does block scope mean?

Answer 2

the variable only exists within the block

Question 3

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

Answer 3

blocked-scope

Question 4

What is the difference between let and const?

Answer 4

let variables can be updated but not re-declared; const variables can neither be updated nor re-declared.

Question 5

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

Answer 5

you can mutate the value of the const read-only reference but you cannot reassign it or redeclare it

Question 6

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

Answer 6

for global use var, for block-scope use let/const

Question 7

What is the syntax for writing a template literal?

Answer 7

wrap text in backticks

Question 8

What is “string interpolation”?

Answer 8

${variable_name}

Question 9

What is destructuring, conceptually?

Answer 9

assigning properties of objects to variables

Question 10

What is the syntax for Object destructuring?

Answer 10

const { property1: variable1, property2: variable2 } = object;

Question 11

What is the syntax for Array destructuring?

Answer 11

const [x, y, z] = array

Question 12

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

Answer 12

the name is on the right of assignment operator for CREATING objects/arrays.
the name is on left for DESTRUCTURING objects/arrays.

Question 13

What are the three states a Promise can be in?

Answer 13

pending, fulfilled, rejected

Question 14

How do you handle the fulfillment of a Promise?

Answer 14

Promise.prototype.then()

Question 15

How do you handle the rejection of a Promise?

Answer 15

Promise.prototype.catch()

Question 16

What is Array.prototype.filter useful for?

Answer 16

Creating a new array while excluding some elements.

Question 17

What is Array.prototype.map useful for?

Answer 17

Creating a new array containing the transformed elements of another.

Question 18

What is Array.prototype.reduce useful for?

Answer 18

Combining the elements of an array into a single value.

Question 19

What is “syntactic sugar”?

Answer 19

designed to make things easier to read or to express

Question 20

What is the typeof an ES6 class?

Answer 20

function

Question 21

Describe ES6 class syntax.

Answer 21

Class className {
constructer (parameters) {

}
method( ) { }
}

Question 22

What is “refactoring”?

Answer 22

the process of restructuring existing computer code without changing its external behavior