ES6

Question 1

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

Answer 1

Code blocks are denoted with curly brace brackets. Some examples include function code blocks, conditional statements, loop code blocks.

Question 2

What does block scope mean?

Answer 2

The variable is only accessible within that code block.

Variables declared using var are accessible outside of a code block except for function code blocks

Question 3

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

Answer 3

Block-scoped

Question 4

What is the difference between let and const?

Answer 4

‘let’ can be reassigned while ‘const’ cannot

Question 5

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

Answer 5

The variable has the same memory address as its value, referring to a certain array. The array is mutable but the location in memory remains constant
The name binding cannot be changed
The array remains constant, not the elements within it

Question 6

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

Answer 6

Rather than use ‘var’, use ‘const’ or ‘let’. If the variable is going to be changed from its initial value, use ‘let’

usually default to ‘const.’ If there is problems in the future, change to ‘let’

Question 7

What is the syntax for writing a template literal?

Answer 7

backtick $ { } backtick

Question 8

What is “string interpolation?”

Answer 8

Substituting parts of a string with the values of variables or expressions

Question 9

What is destructuring, conceptually?

Answer 9

Taking the properties of an object and assigning them to multiple variables in one go

Question 10

What is the syntax for Object destructuring?

Answer 10

const thing = {
this: 1,
that: 2,
};

const { this, that } = thing;

Question 11

What is the syntax for Array destructuring?

Answer 11

const things = [
{this: 1, that 1},
{this: 2, that 2}
]

const [thing2, thing3] = things

Question 12

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

Answer 12

With destructuring, curly brackets on the left hand side of equal sign
With creating, curly brackets on the right hand side of equal sign

Question 13

What is the syntax for defining an arrow function?

Answer 13

(parameter 1, parameter 2) => {code block}

Question 14

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

Answer 14

The arrow function returns value of the expression of the body without the curly brace (an implicit return)

Question 15

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

Answer 15

While regular function syntax will create a new function that creates its own this, arrow functions do not create their own this. Instead, it will be lexically scoped, so it will find the this for the context that it is within
They don’t create their own this binding
Value of this is defined at definition time, not at call time (which is the case for traditional ES5 functions)
If you can’t see where it’s being called, this might be referring to the global window

Question 16

What is a CLI?

Answer 16

Command Line Interface

Question 17

What is a GUI?

Answer 17

Graphical User Interface

Question 18

Give at least one case for each of the commands used in this exercise.

Answer 18

• man: manual
• cat: concatenate files
• ls: list directory contents
• pwd: print working directory
• echo: display text
• touch: change file timestamps
• mkdir: make directories
• mv: move files
• rm: remove files
• cp: copy files

Question 19

What are 3 virtues of a great programmer?

Answer 19

Laziness, impatience, hubris

Question 20

What are the 3 states a Promise can be in?

Answer 20

• Pending- promise is created, promise hasn’t come back yet
• Fulfilled- promise was completed
• Rejected- promise had an error

Question 21

How do you handle the fulfillment of a Promise?

Answer 21

Pass a function as the first argument to a .then method on the Promise

Question 22

How do you handle the rejection of a Promise?

Answer 22

Either pass a function as the second argument to a .then method, or a function as the only argument in a .catch method

Question 23

What is ‘array.prototype.filter’ useful for?

Answer 23

Helps with extracting certain values out of an array

Question 24

What is array.prototype.map useful for?

Answer 24

It is useful for manipulating/transforming elements inside an array (and getting a new array)

Question 25

What is Array.prototype.reduce useful for?

Answer 25

It is useful for “aggregating” elements in an array into a single entity, and the aggregation does not have to be simply mathematical operations on numbers. It can be used any time we have an array of things that we want to do stuff to, and we want the end result to be a single thing.

Question 26

What is “syntactic sugar”?

Answer 26

Syntax that makes code easier/”sweeter” to read for humans but can be removed without affecting the capabilities of the language

Question 27

What is the ‘typeof’ an ES6 class?

Answer 27

function

Question 28

Describe ES6 class syntax.

Answer 28

• ## class keyword followed by the name of the class, then curly braces. Inside the braces, a function constructor which is called when a new object of that class is instantiated. The constructor function is followed by method definitions written like function definitions```javascript
  class Student {
  constructor(firstName, lastName) {
  this.firstName = firstName;
  this.lastName = lastName;
  }
  getFullName() {
  return ${this.firstName} ${this.lastName};
  }
  }
  ~~~

Question 29

How are ES Modules different from CommonJS modules?

Answer 29

They have a different syntax (import and export instead of require() and module.exports)

Question 30

What kind of modules can Webpack support?

Answer 30

• EcmaScript modules (ES)
• CommonJS
• AMD

Question 31

What does ‘fetch()’ mean?

Answer 31

A Promise that only resolves to reject if there is a network error that prevents the request from completing, otherwise a response object

Question 32

What is the default request method used by ‘fetch()’?

Answer 32

‘GET’

Question 33

How do you specify the request method (‘GET’, ‘POST’, etc.) when calling ‘fetch’?

Answer 33

After the URL, specify in the options object { method: 'GET' }