ES6

Question 1

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

Answer 1

block scope

Question 2

difference between const and let?

Answer 2

1. Const can’t be mutated let is mutable.
   
   2. They can’t be redeclared in the same scope.
   3. Const has to be initialized when declared.

Question 3

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

Answer 3

youre not redefining the variable, the value can be mutated.

Question 4

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

Answer 4

How should you decide on which type of declaration to use?
If the variable is not going to be reassigned, use ‘const’. If it will be reassigned, then use ‘let’

var is dead unless you want a global variable

Question 5

syntax for template literals

Answer 5

1. Similar to a string, but using back-ticks and a JavaScript expression

Question 6

What is “string interpolation”?

Answer 6

Embedding variables and expressions with their values.

Question 7

What is the syntax for Object / array destructuring?

Answer 7

const {propertName: variableName, , ,} = Object;

const [arrayElements, , , , ] = array;

Question 8

whats the difference between destructuring and creating obj/array literals?

Answer 8

the properties and values are on the left side of the assignment operator when destructuring.

Question 9

syntax for arrow function?

Answer 9

let add = (x,y) => x + y;

Question 10

what happens when an arrow functions body is w/o curly braces?

Answer 10

the result is automatically returned.

Question 11

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

Answer 11

at definition time.

Question 12

What is a code block?

Answer 12

a block of code within curly braces

Question 13

what does block scope mean?

Answer 13

an area within the block where variables can be referenced.

Question 14

What is the JavaScript event loop?

Answer 14

The Event Loop is a queue of callback functions. Takes the first thing on the callback queue and puts it back on the stack if the stack is empty

Question 15

what is the difference between blocking and non blocking with respect to how code is executed?

Answer 15

Blocking is when the execution of additional JavaScript in the Node.js process must wait until a non-JavaScript operation completes.
Non-blocking methods execute asynchronously.

Question 16

What are the three states a promise can be in?

Answer 16

Fulfilled, rejected, pending

Question 17

How do you handle the fulfillment and rejection of a promise?

Answer 17

.then() and .catch()

Question 18

What is Array.prototype.filter useful for?

Answer 18

to create a new array with specific elements from the original array based on truthy values.

Question 19

What is Array.prototype.map useful for?

Answer 19

to create a new array containing the transformed elements of another array.

Question 20

what is Array.prototype.reduce useful for?

Answer 20

combining the elements of an array into a single value.

Question 21

Syntactic sugar

Answer 21

Code that is designed to be easier to read or write.

Question 22

typeof es6 class?

Answer 22

function

Question 23

Describe es6 class syntax

Answer 23

class keyword, name of class, curly braces for the class body and in the body there are defined prototype methods.

Question 24

refactoring?

Answer 24

Restructuring existing code to be easier to read and not changing the behavior

Question 25

webpack

Answer 25

a package that can take your modules or packages that incorporates a bundled main.js file with all of it.

Question 26

add a devDependency to a package?

Answer 26

npm install –save-dev

Question 27

what is an npm script?

Answer 27

An NPM script are typically commands, or a string of commands, which would normally be entered at the command line in order to do something with your application.

Question 28

execute webpack ?

Answer 28

npm run build

Question 29

difference between es modules and commonJS modules?

Answer 29

• ES is the standard for JS, CommonJS is for Node.
  
  • ES modules has specific keywords. Import, Export, Default..
  • With CommonJS you call a function.

Question 30

What kind of modules can webpack support?

Answer 30

ES modules, commonJS modules AMD modules