ES-6

Question 1

what is a code block? what are examples of a code block?

Answer 1

chunk of code to define statements to be executed together indicated by curly braces

ex. functions, for loops, conditionals (if statements)

Question 2

what does block scope mean?

Answer 2

block scope refers to the area within code block

variables exist only within the corresponding 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

const keyword creates block-scoped variables whose values can’t be reassigned

let - mutable, const- immutable

Question 5

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

Answer 5

value of the const variable is mutable

Question 6

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

Answer 6

consider if the variable needs to be reassigned later on within the block scope - if so, let

const - no reassignment
let - reassignment

favor const over let - when you are stuck in a situation where const won’t work, use let

Question 7

what is destructuring, conceptually?

Answer 7

allows you to unpack values from arrays, or properties from objects, into distinct variables

Question 8

what is the syntax for Object destructuring? ** { } curly braces for destructuring isn’t considered a code block

Answer 8

const/let keyword,
curly braces,
variable names within curly brace,
assignment operator,
variable

Question 9

what is the syntax for Array destructuring? ** { } curly braces for destructuring isn’t considered a code block

Answer 9

const/let keyword,
brackets,
variable names,
assignment operator,
variable

Question 10

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

Answer 10

destructuring, check for variable name at the end

or if there is no variable name following const/let

Question 11

what is the syntax for writing a template literal?

Answer 11

using back ticks ` `, ${ } for variables

Question 12

what is “string interpolation?”

Answer 12

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

Question 13

what is the syntax for defining an arrow function?

Answer 13

one param - param => expression (for anonymous)
multiple params - (param1, param2) => expression, requires parantheses
multiple statements - require body brackets and return

Question 14

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

Answer 14

it will return a value without the return keyword (implicit return)

Question 15

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

Answer 15

the this value is determined by 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

promise.then(onFulfilled[,onRejected])

or

promise.then(value => {//code for fulfillment}

Question 18

how do you handle the rejection of a promise?

Answer 18

promise.then

or promise.catch

Question 19

what is syntactic sugar?

Answer 19

syntax that is designed to make things easier to read or to express

Question 20

what is the type of an ES6 class?

Answer 20

function

Question 21

describe ES6 class syntax

Answer 21

class declaration, class name

constructor with parameter(s), followed by code block

followed by any functions you want to implement

Question 22

what is refactoring?

Answer 22

process of restructuring existing computer code without changing its external behavior/output

Question 23

how are ES modules different from CommonJS modules?

Answer 23

ES modules syntax are even more compact than CommonJS

structure can be statically analyzed

their support for cyclic dependencies are better than CommonJS

Question 24

what kind of modules can Webpack support?

Answer 24

EMCAScript, CommonJS, AMD (asynchronous module definition)

Question 25

what is Webpack?

Answer 25

a tool that lets you bundle your JS applications

Question 26

how do you add a DevDependency to a package?

Answer 26

npm install –save-dev

Question 27

what is an NPM script?

Answer 27

supports number of built-in scripts and their preset lifecycle events

Question 28

how do you execute Webpack with npm run?

Answer 28

add an npm script

npm run build