ES6

Question 1

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

Answer 1

Surrounded by brackets with code written inside. Functions, loops, if conditionals

Question 2

What does block scope mean?

Answer 2

Only available within that block

Question 3

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

Answer 3

Block-scope

Question 4

What is the difference between let and const?

Answer 4

Let - can be reassigned. Const - cannot be reassigned. “=”

Question 5

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

Answer 5

We are not reassigning the value

Question 6

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

Answer 6

You let if you need the value to change (reassigned) and const if the value will always be the same.

Question 7

What is the syntax for writing a template literal?

Answer 7

Using backticks around the string and a dollar sign with curly brace around the variable

Question 8

What is “string interpolation”?

Answer 8

Substituting part of a string with variables.

Question 9

What is destructuring, conceptually?

Answer 9

To take pieces of a more complex structure (elements from array, prop from obj) and assign them to variables. Assigning properties of an object or an array to individual variables

Question 10

What is the syntax for Object destructuring?

Answer 10

const object with key value pairs assigned to a variable

Question 11

What is the syntax for Array destructuring?

Answer 11

const with square brackets with variable names with an assignment operator and the array it’s coming from

Question 12

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

Answer 12

Objects or array is on the left of the assignment operator for destructuring while objects or array is on the right of the assignment operator when creating an object/array literal

Question 13

What is the syntax for defining an arrow function?

Answer 13

Variable keyword, var name, parameters (necessary if zero parameter, optional if one parameter and necessary if more than one parameter), arrow, curly braces (only if a statement)

Question 14

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

Answer 14

You can only have one line of code. Has to be an expression.

Question 15

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

Answer 15

Is based on when the arrow function is defined. The value of ‘this’ in its parent code block. If the parent is an arrow function as well, it keeps going up.

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

catch()

Question 19

What is Array.prototype.filter useful for?

Answer 19

To find things within an array

Question 20

What is Array.prototype.map useful for?

Answer 20

To apply a transformation to each element in an array

Question 21

What is Array.prototype.reduce useful for?

Answer 21

To getting a single value from combining elements from an array

Question 22

What is “syntactic sugar”?

Answer 22

Syntax within a programming language that makes things easier to read or to express.

Question 23

What is the typeof an ES6 class?

Answer 23

Function

Question 24

Describe ES6 class syntax

Answer 24

Keyword class followed by the name of the class with a code block. A constructor in the function (optional) with methods below it.

Question 25

What is “refactoring”?

Answer 25

The process of restructuring existing code without changing its external behavior

Question 26

How are ES Modules different from CommonJS modules?

Answer 26

ES module syntax is more compact and can export multiple things. Keywords are different - import/export vs require. Static (ES Module - it will look at the code and remove any unused portions) vs dynamic (CommonJS module). ES6 is ‘official’

Question 27

What kind of modules can Webpack support?

Answer 27

ECMAScript, CommonJS and AMD modules.