ES6 JS

Question 1

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

Answer 1

The code block is a location where we write codes between the curly braces.
{}

Question 2

What does block scope mean?

Answer 2

It restricts the variable that is declared inside the specific block from being accessed from outside of the block

Question 3

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

Answer 3

blocked-scope

Question 4

What is the difference between let and const?

Answer 4

You can change the value assigned to the let keyword while const you cannot.

Question 5

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

Answer 5

Because you are not reassigning a different array to the const variable, you are simply adding a value to the same array
The object is still mutable when it’s assigned to a variable so you can add data to it

Question 6

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

Answer 6

If you need to reassign values to the variable, then you should use let

Question 7

What is the syntax for writing a template literal?

Answer 7

${variable}

Question 8

What is “string interpolation”?

Answer 8

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

Question 9

What is destructuring, conceptually?

Answer 9

JS expression that makes it possible to unpack elements from arrays or properties from objects, into distinct variables

It’s how you get object properties or array elements into one line

Question 10

What is the syntax for Object destructuring?

Answer 10

let { property1: variable1, property2: variable2 } = object;

Question 11

What is the syntax for Array destructuring?

Answer 11

let [x, y, z] = variableName

Question 12

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

Answer 12

you have the variable name to the left of the ‘=’ operator when creating object/array literals. Whereas, the variable name is on the right when destructuring.

Question 13

What is the syntax for defining an arrow function?

Answer 13

parameter => expression
param => { statement }

Question 14

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

Answer 14

It has an implicit return
You will need a curly braces when you have multiple lines of statement with a return statement

Question 15

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

Answer 15

parent’s code block and is being determined at definition time

Question 16

What is a CLI?

Answer 16

Command-line interface
to receive commands from a user in the form of lines of text

Question 17

What is a GUI?

Answer 17

Graphical user interface
For users to interact with graphical icons

Question 18

Give at least one use case for each of the commands listed in this exercise.
man, cat, ls, pwd, echo, touch, mkdir , mv, rm, cp

Answer 18

man - interface to the system reference manuals
cat - concatenate files and print on the standard output
ls - list directory contents
pwd - print name of current/working directory
echo - display a line of text
touch - change file timestamps
mkdir - make directories
mv – move (rename) files
rm - remove files or directories
cp - copy files and directories

Question 19

What are the three states a Promise can be in?

Answer 19

pending, fulfilled, or rejected

Question 20

How do you handle the fulfillment of a Promise?

Answer 20

.then() - pass in callback function
When the promise is fulfilled, this code is used to execute the function

Question 21

How do you handle the rejection of a Promise?

Answer 21

.catch() - pass in a callback function, if the promise is rejected, this code will be executed

Question 22

What is Array.prototype.filter useful for?

Answer 22

It creates a new array filled with elements that pass a test provided by a function

Question 23

What is Array.prototype.map useful for?

Answer 23

you can format it into a string

Question 24

What is Array.prototype.reduce useful for?

Answer 24

we can use it to turn the array into an object
return a single value from an array

Question 25

What is “syntactic sugar”?

Answer 25

That allows code to become easier to read or friendly but at the cost of flexibility

Question 26

What is the typeof an ES6 class?

Answer 26

object

Question 27

Describe ES6 class syntax.

Answer 27

class ClassName {
constructor(param) {
// stuff
}
methodName(param) {
// more stuff
}
}

Question 28

What is “refactoring”?

Answer 28

Process of restructuring existing computer code without changing its functionality

Question 29

How are ES Modules different from CommonJS modules?

Answer 29

each dependency is stored in its file for ES Modules. This allows developers to better control how their dependencies are used. Whereas, CommonJS keeps all the files in one file named node_modules

ES6 has a greater functionality attached to it

Question 30

What kind of modules can Webpack support?

Answer 30

ESMAScript modules
CommonJS modules
amd MODULES