JavaScript ES6

Question 1

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

Answer 1

A code block refers to the code within the curly braces.

Examples of code blocks include functions, loops, and conditionals.

Question 2

What does block scope mean?

Answer 2

Block scope defines the availability of a variable to only within it’s code block

Question 3

What is the scope of a variable declared withconstorlet?

Answer 3

Block scope

Question 4

What is the difference betweenletandconst?

Answer 4

let can be reassigned

const cannot be reassigned

Question 5

Why is it possible to.push()a new value into aconstvariable that points to anArray?

Answer 5

Pushing is changing the value to the array in memory space, but not reassigning the reference value.

Question 6

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

Answer 6

Prefer const, unless a variable needs to be mutated.

Question 7

What is the syntax for writing a template literal?

Answer 7

Back ticks start and end `` with any variables starting with dollar sign wrapped in curly braces.

Hello ${name}!

Question 8

What is “string interpolation”?

Answer 8

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

Question 9

What is destructuring, conceptually?

Answer 9

Assignment of javascript object properties to variables

Question 10

What is the syntax forObjectdestructuring?

Answer 10

Variable declaration
Curly brace with variable(s) 
*If renaming propertyname : new name*
Assignment Operator
Object to destructure

e.g.
let { firstName, lastName } = person;

Question 11

What is the syntax forArraydestructuring?

Answer 11

Variable declaration
Square Bracket with variable(s)
Assignment Operator
Array to destructure

Question 12

How can you tell the difference between destructuring and creatingObject/Arrayliterals?

Answer 12

Destructuring will have the variables in brackets or curly braces on the left side of the assignment operator, and an existing array or object on the right hand side

Question 13

What is the syntax for defining an arrow function?

Answer 13

• Variable keyword
• Variable name
• Parameters
• Arrow
• Bracket (Only required if statement)

Question 14

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

Answer 14

• The function can only have one line of code

- The code block must be an expression (code that resolves to value)

Question 15

How is the value ofthisdetermined within an arrow function?

Answer 15

• The value of this is determined by it’s parent code block (outward with arrow functions)

Question 16

When is it necessary to have parenthesis for parameters?

Answer 16

• 0 or 2+ mandatory

- 1 not mandatory

Question 17

What are the three states a Promise can be in?

Answer 17

• Pending: initial state, neither fulfilled nor rejected
• Fulfilled: Successul operation
• Rejected: Failed operation

Question 18

How do you handle the fulfillment of a Promise?

Answer 18

• then() method attaches fulfillment and rejection handlers to the promise, and returns a new promise

Question 19

How do you handle the rejection of a Promise?

Answer 19

• catch() method appends a rejection handler

Question 20

What isArray.prototype.filteruseful for?

Answer 20

Returning a filtered array

Question 21

What isArray.prototype.mapuseful for?

Answer 21

Creating a new array with all of the previous arrays elements modified

Question 22

What isArray.prototype.reduceuseful for?

Answer 22

Returning the sum of an array

Question 23

What is “syntactic sugar”?

Answer 23

An alternative style on an existing syntax to make the language more clear for human use.

Question 24

What is thetypeofan ES6 class?

Answer 24

Function

Question 25

Describe ES6 class syntax.

Answer 25

class Example
   constructor(a, b, c) {
      this.a = a
      this.b = b
      this.c = c
   },
methodName() {}

Question 26

What is “refactoring”?

Answer 26

Restructuring existing code without changing its external behavior.

Question 27

What is Webpack?

Answer 27

Webpackis astatic module bundlerfor modern JavaScript applications

Question 28

How do you add adevDependencyto a package?

Answer 28

npm install –save-dev [package name]

Question 29

What is an NPM script?

Answer 29

• Commands that would typically be entered in command line to perform an action with your project
• NPM script is stored within your package.json file under “scripts”

Question 30

How do you execute Webpack withnpm run?

Answer 30

In package.json add to scripts:
“build”: “web pack”

npm run build

Question 31

How are ES Modules different from CommonJS modules?

Answer 31

ESM is statically analyzable, which allows for tree shaking (process that removes unused code from bundles)

Enhanced syntax (import export vs require)

ESM is official

Question 32

What kind of modules can Webpack support?

Answer 32

ECMAScript Modules
CommonJS Modules
AMD modules

Question 33

What doesfetch()return?

Answer 33

APromisethat resolves to aResponseobject.

Question 34

What is the default request method used byfetch()?

Answer 34

GET

Question 35

How do you specify the request method (GET,POST, etc.) when callingfetch?

Answer 35

Using request options, as a second argument with a specified method.

Question 36

What must the return value of myFunction be if this expression is possible:

myFunction()();

Answer 36

myFunction calls a function and that inner function executes immediately after

Therefore, myFunction’s return must be a function

Question 37

What does this code do?

const wrap = value => () => value;

Answer 37

Returns a value

Question 38

In JavaScript, when is a function’s scope determined; when it is called or when it is defined?

Answer 38

Upon definition

Question 39

What allows JavaScript functions to “remember” values from their surroundings?

Answer 39

A closure