ES6

Question 1

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

Answer 1

block scope

Question 2

What does block scope mean?

Answer 2

Within the block

Question 3

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

Answer 3

define within { … }, if, for, while,…

Question 4

What is the difference between let and const?

Answer 4

let can be reassigned
const cannot be assigned

Question 5

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

Answer 5

const is mutable ONLY if it’s object

Question 6

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

Answer 6

if you want to reassign value in the future use let, otherwise use const.

Question 7

What is the syntax for writing a template literal?

Answer 7

backtick () then ${JavaScript Expression}

Question 8

What is “string interpolation”?

Answer 8

to create strings by doing substitution of placeholders

Question 9

What is destructuring, conceptually?

Answer 9

convenience way to extract property values of an object (in 1 line)

Question 10

What is the syntax for Object destructuring?

Answer 10

var/let/const { property1:alias_name = ‘default_value’ , property2, … } = object;

Question 11

What is the syntax for Array destructuring?

Answer 11

var/let/const [ element1st, element2nd, …. , element#nth ] = array;

Question 12

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

Answer 12

{ } or [ ] is on the left side of = then destructuring

Question 13

What is the syntax for defining an arrow function?

Answer 13

( ) => { }

Question 14

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

Answer 14

no code block = implicit return (return without return statement)
with { }, will require return keyword to actually return value.
{ } allows for multilines code block

Question 15

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

Answer 15

the value is determine at the definition time, (parent code block)

Question 16

What is “syntactic sugar”?

Answer 16

syntax within a programming language to make things easier to read or to express

Question 17

What is the typeof an ES6 class?

Answer 17

function

Question 18

Describe ES6 class syntax.

Answer 18

class ClassName {
constructor(…) {
//this.parameter = parameter;
}
methodName(…) {
//definition
}
}

Question 19

What is “refactoring”?

Answer 19

the process of restructuring existing computer code without changing its external behavior, intend to improve the design, structure, and/or implementation of the software while preserving its functionality.
- improve code readability and reduced complexity.

Question 20

How are ES Modules different from CommonJS modules?

Answer 20

commonJS:
- compact syntax
- designed for synchronous loading
- main use: server
ES modules:
- more compact syntax than common JS
- have support for asynchronous loading and configurable module loading

Question 21

What kind of modules can Webpack support?

Answer 21

ECMAScript modules
CommonJS modules
AMD modules
Assets
WebAssembly modules
many more (with Loaders)

Question 22

What is React?

Answer 22

a JS library for creating user interfaces.

Question 23

What is a React element?

Answer 23

an object that virtually describes the DOM nodes that a component represents

Question 24

How do you mount a React element to the DOM?

Answer 24

root = ReactDOM.createRoot(“querySelectedContainer”)
root.render(ReactElement)

Question 25

What is Babel?

Answer 25

JavaScript compiler. Toolchain that is mainly used to convert ES 2015+ code into backward compatible version of JS in current and older browsers or environments

Question 26

What is a Plug-in?

Answer 26

a software component that adds a specific feature to an existing program.

Question 27

What is a Webpack loader?

Answer 27

transformations that are applied to the source code of a module, allow you to pre-process files as you import or load them.

Question 28

How can you make Babel and Webpack work together?

Answer 28

install the packages, and make sure the config is correct within the package.json