ES6

Question 1

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

Answer 1

A series of grouped code statements in curly braces. The body of a for loop, while loop, if statement, function.

Question 2

What does block scope mean?

Answer 2

Variables declared within a containing code block are only accessible within that containing 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

A let variable can be reassigned another value after declaration
A constant can not be reassigned another value after declaration

Question 5

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

Answer 5

Although a constant can not be reassigned another value, if it points to an array, that array can be manipulated. Since the constant still points to the same array, reassignment is not occurring.

Question 6

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

Answer 6

If you plan on never reassigning another value, then declare a constant.
If you plan on reassigning another value, then declare a let variable.

Question 7

What is destructuring, conceptually?

Answer 7

• breaking up the structure

- in JavaScript, it is a shortcut for assigning array values and object properties to variables

Question 8

What is the syntax for Object destructuring?

Answer 8

variable keyword followed by opening curly brace, property name (with optional colon and variable name), closing curly brace, assignment operator, and object name
let {
   firstName: fname, 
   lastName: lname
} = person;

Question 9

What is the syntax for Array destructuring?

Answer 9

variable keyword followed by opening bracket, variable names in indexed order, closing bracket, assignment operator, array name
let [x, y, z] = arrayName

Question 10

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

Answer 10

In destructuring, [] and {} are on the left hand side of the assignment operator and the name of the array or object is on the right hand side

Question 11

What is the syntax for writing a template literal?

Answer 11

backtick, string, placeholder expressions, backtick

Fifteen is ${a + b} and not ${2 * a + b}.

Question 12

What is “string interpolation”?

Answer 12

replacing placeholders with values in a template literal

Question 13

What is the syntax for defining an arrow function?

Answer 13

( ) => { }
parameter (parenthesis if more than one parameter), followed by equal sign/arrow, followed by expression (optional curly braces/ return statement)

Question 14

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

Answer 14

It returns the result of the expression without a return statement

Question 15

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

Answer 15

It comes from the outer scope of its container in its definition, since it does not have its own reference to ‘this’ at call time like other functions

Question 16

What is Array.prototype.filter useful for?

Answer 16

filtering an array into another array

Question 17

What is Array.prototype.map useful for?

Answer 17

changing each element of an array, and putting those elements in a new array

Question 18

What is Array.prototype.reduce useful for?

Answer 18

combining each element of an array into one element

Question 19

What is “syntactic sugar”?

Answer 19

syntax which is easier to read but doesn’t change functionality

Question 20

What is the typeof an ES6 class?

Answer 20

function

Question 21

Describe ES6 class syntax.

Answer 21

class className {
   constructor(parameter) {
      this.parameter = parameter
   }
   method() {
   }
}

Question 22

What is “refactoring”?

Answer 22

restructuring code without altering its behavior

Question 23

What is Webpack?

Answer 23

a module bundler for JavaScript applications

Question 24

How do you add a devDependency to a package?

Answer 24

npm install –save-dev

Question 25

What is an NPM script?

Answer 25

scripts (command line commands) in package.json that run at certain times of production

Question 26

How do you execute Webpack with npm run?

Answer 26

npm run

Question 27

How are ES Modules different from CommonJS modules?

Answer 27

ES Modules use import __ from ‘path’ and export default

CommonJS Modules use require(‘path’) and module.exports =

Question 28

What kind of modules can Webpack support?

Answer 28

both EcmaScript and CommonJS and AMD modules

Question 29

default export

Answer 29

can import without curly braces, and can name whatever you want

Question 30

named exports

Answer 30

{} are needed and need to import by name

Question 31

What is Babel?

Answer 31

toolchain to convert ECMAScript 2015 code into a backwards compatible version of JavaScript

Question 32

What is a Plug-in?

Answer 32

component that adds a feature to an existing program

Question 33

What is a Webpack loader?

Answer 33

a transformation applied to the source code of a module (can transform files from one language to Javascript)

Question 34

How can you make Babel and Webpack work together?

Answer 34

install babel loader