ES6

Question 1

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

Answer 1

-Grouped zero or more statements within curly braces

Question 2

What does block scope mean?

Answer 2

-A block scope is the area within if, switch conditions or for and while loops.

Question 3

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

Answer 3

-Those variables exist only within the corresponding block.

Question 4

What is the difference between let and const?

Answer 4

-Variable declared by let are mutable but variables declared by const are immutable

Question 5

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

Answer 5

• The const keyword ensures that the variable it creates is read-only
• However, it doesn’t mean that the actual value to which the const variable reference is immutable

Question 6

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

Answer 6

-For read-only variables, use const

Question 7

What is the syntax for writing a template literal?

Answer 7

• Use backticks instead of single or double quotes

- To substitute a variable and an expression, use this block: ${variable_name}

Question 8

What is “string interpolation”?

Answer 8

-String interpolation allow you to embed variables and expressions in a string. The JavaScript engine will automatically replace these variables and expressions with their values.

Question 9

What is destructuring, conceptually?

Answer 9

-Unpacking values from objects and arrays into variables

Question 10

What is the syntax for Object destructuring?

Answer 10

• Variable declaration
• Curly braces
• The identifier before the colon (:) is the property of the object and the identifier after the colon is the variable
• Equal sign and object name

Question 11

What is the syntax for Array destructuring?

Answer 11

• Variable declaration
• Square brackets with variable names separated by commas
• Equal sign and object name

Question 12

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

Answer 12

• When creating object/array literals, we assign the object to the variable
• When destructuring, we assign the object to the variable

Question 13

What is the syntax for defining an arrow function?

Answer 13

• Use the (…args) => expression; to define an arrow function
• Use the (…args) => { statements } to define an arrow function that has multiple statements

Question 14

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

Answer 14

-If there are no curly braces, the expression is automatically returned from the arrow function

Question 15

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

Answer 15

-An arrow function captures the this value of the enclosing context instead of creating its own this context

Question 16

What are the three states a Promise can be in?

Answer 16

• pending
• fulfilled
• rejected

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

• .then()

- .catch()

Question 19

What is “syntactic sugar”?

Answer 19

-In computer science, syntactic sugar is syntax within a programming language that is 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 keyword, name of class
• Constructor keyword with argument followed by code block where properties of an instance are initialized
• function definition without the function keyword

Question 22

What is “refactoring”?

Answer 22

-Process of restructuring existing code without changing its external behavior